There's going to be a short epilogue; 1000 words max. As you've probably already noticed, all the chapters, as well as the epilogue, are named after the characters it focuses on (more or less).

Butters went over everything in his head over and over again, trying to find the right course of action. Kyle just sat there, waiting for the blond to answer his question until, finally, he did. He decided that it would be better to deny any knowledge of this, but still try to help Kyle figure out the truth on his own.

Leopold: ...I don't know, but I could help you find out.

"Right. That's why we've been sitting here in silence for almost five minutes."

Kyle: Butters, don't lie to me. Actually, just don't lie to anyone. You sucked at it when we were kids and you suck at it now. If you're not going to tell me, I'll just have to figure it out on my own. Goodbye, Butters.

Kyle left Butters' house and slammed the door behind him, as a clear sign of frustration.

"...That went well."

Butters knew that Kyle would probably never speak with him again, but only time would tell if he had made the right choice when answering his question.

"Now what do I do? I can't just ask Kenny directly; he would never tell me. Butters isn't an option, Cartman is a retard... If only Stan was... Stan would know what to do. Stan always knew what to do."

Kyle suddenly had an idea, but it was quickly crushed by his moral compass; however, he still wondered in the back of his mind if it was possible. He could simply follow Kenny (without being seen) every time he went to see Stan at the hospital and listen to his "conversations" with him to see if he was consistent. If he was, then the truth would be obvious.

He tried to turn his thoughts in another direction; he didn't want to even consider spying on his best friend, much less actually convince himself to do it.
As his mind wandered, his thoughts soon turned into reasons as to why he was so obsessed with Kenny and why he was so angry when he saw Butters and Kenny together. Why did he feel this way? Was it concern for Kenny? Was it disgust for their relationship (or lack thereof)? Or was it something else; something personal?

He wasn't ready to face the truth, so before he realized what it was, his thoughts once again shifted; this time towards the reason as to why Kenny was so obsessed with Stan. They were good friends, but not even Kyle himself, his best friend, was visiting him nearly every single day and talking to him. The most obvious answer was guilt, so Kyle decided to test that theory. He would need to see what happened to Kenny all those years ago and find a correlation between what happened to Kenny and what happened to Stan.

"Who could tell me?"

Kyle was getting nowhere. He needed someone who was smart, close to Kenny and who would tell him what happened.

"I could ask Kevin, but he ran away..."

Six years ago, Kenny had convinced his parents to tell the town that Kevin had ran away, to prevent anyone from asking too many questions about a sensitive subject. It worked; the entire town believed it and, due to the police's severe incompetence, no evidence was found (or at least recorded) that proved otherwise.

"When did Kevin run away? And why?"

Kyle finally had something to go on. He didn't know how it was connected to everything else, but he had a feeling that if he followed this lead, it would take him to the truth.

"I just hope I'm right about this..."

Kyle went home, as there was nothing else he could do for today. The sun was setting in the horizon, the adults were returning home, and he needed to talk to Kenny's parents, his sister and Kenny himself separately.

"...I've seen this before..."

Stan: This is all your fault! You did this to me!
Kenny: I'm sorry... I'm sorry...
Kevin: You did this to us. You killed me!

"I'm sorry..."

Kyle: You don't deserve to live!

As everyone around him tried to grab him while turning into enormous, deformed monsters, Kenny suddenly woke up in a cold sweat.

"...Another sleepless night for me... I guess I deserve it."

Kenny lied on his side and cried all through the night, with the voices from his nightmare still echoing inside his head. He truly believed what he heard in his nightmares, and it was messing him up.
He believed that he didn't deserve to live, but he was unable to die. He believed that he was responsible for what happened to Stan, but he was unable to fix it. He believed that he was responsible for what happened to Kevin, but there was no way to fix that. There was simply nothing that he could do but live out the rest of his life thinking that he killed his brother and put one of his best friends in the hospital.

By the time Kenny's parents and sister woke up, Kenny had already made and eaten some breakfast, showered and was ready for school. However, his mind wasn't all there. Part of him was still thinking about his nightmare and agreeing with what was said, while the other part was trying to forget it and snap him to reality. Unfortunately, the former side won and Kenny spent the rest of the day replaying his nightmare in his head. His distraction was clear to everyone, but only Kyle approached him. Before he said anything, he looked around to see if Butters was nearby. Thankfully, Kenny had stayed behind for a while, even though nearly everyone else had left, so there was nobody who would bother Kyle while he talked to him.

Kyle: Hey, Kenny.

"What do you want?"

Kenny: ...Hey.
Kyle: ...What's wrong?
Kenny: It's nothing- I mean, nothing's wrong.

"...Wow, you're even worse at this than Butters."

Kyle: Kenny, I'm your friend. You can talk to me about anything.

"Really? Anything? Do you want me to tell you how I put your best friend in the hospital and got my brother killed, all in the same day? Or how I've had a major crush on you for the past seven years or so?"

Kyle: ...Is it about the prom? There are still girls who don't have dates, you know. You just have to ask one of them to go with you.

"For fuck's sake."

Kenny: No, Kyle, it's not about the fucking prom. Just leave me alone.
Kyle: Alright... Sorry.

"I'd ask you about Kevin, but now I'm afraid you'll hit me."

Kyle felt bad that he was unable to help Kenny, but he decided to go talk to his sister and parents anyway, as he had planned. Kenny's sister told him that Kevin had run away and that he left a note behind, whereas his mother denied the existence of such a note and his father disagreed on the contents of said note. It was obvious that someone was lying about something, but they all agreed on the exact date that he ran away. Kyle had heard the date before, but he couldn't quite remember why it was important.

"Maybe Kenny visits Stan often because his brother is at the same hospital."

Kyle walked all the way to the hospital and approached the receptionist.

Kyle: Hey, is there a patient here named "Kevin McCormick"?
Receptionist: I'm sorry, I can't give you that information unless you're a family member.

"This is bullshit."

Kyle: OK. Thanks.

Kyle waited for the receptionist to be called away and checked the computer himself. He searched for "Kevin McCormick", "Kevin" and "McCormick". Every search failed. If Kevin was still in town, he wasn't here.

"Where are you, Kevin?"

Receptionist: Young man, what are you doing?

"Oh shit."

The receptionist, thinking that Kyle was trying to steal patient files, called the police, and Kyle was arrested on the spot. However, since officer Barbrady knew Kyle, he believed him when he said he was just looking for someone. Unfortunately, he couldn't just let Kyle walk out of there; he was going to have to spend the night in jail.

"Well, at least he let me call my mother and tell her I was spending the night at 'a friend's house'... She was pissed that I didn't tell her earlier, but at least she won't kill me when I come home... I hope."

The next day Kyle went straight home from jail. He wasn't going to risk making his mother even more upset than she already was. As soon as he got out of the police station, however, he (literally) bumped into Kenny, who seemed as distracted as he did the previous day.

Kenny: Hey, Kyle. What were you doing in there?
Kyle: I got arrested.
Kenny: ...What?
Kyle: It was nothing. Don't worry.

"You're not even going to tell me why you got arrested?"

Kenny: ...Alright.

"I guess I'd better try again..."

Kyle: So... How are you doing today?
Kenny: I'm fine... By the way... Do you have a... date for the prom?
Kyle: No, not yet.
Kenny: ...I thought you'd be getting a lot of requests from the girls at the school.

"Why would you think something like that?"

Kyle: Yeah, I am, but... I just don't... I don't feel like going with them.
Kenny: Why not? The prom is tomorrow, I thought you'd have a date by now.

"...That's a very good question."

Kyle: ...It's complicated. Look, I gotta go. My mom doesn't know where I spent the night and she'll kill me if I'm not home early today.
Kenny: Sorry... Come on, I'll walk you home.
Kyle: That's alright. I don't want to bother you.
Kenny: It's no problem. I'm going that way anyhow.
Kyle: ...Thanks.

Kenny and Kyle walked in silence, smiling. Their hands touched for a brief moment, almost like they were holding hands and were now letting go, which made both of their hearts flutter and turned their cheeks pink, but they still didn't say anything. They kept on walking, eyes facing down. When they finally arrived at Kyle's, Kyle gave Kenny a big hug and went home, unaware that Kenny was still standing outside, waiting for him to actually close the door. When he noticed this, he smiled, closed the door behind him and, after he actually realized what he felt and did five minutes ago, he panicked.

"...What the fuck just happened?"

Kyle tried to put it out of his mind, but there was no denying it – Something happened between him and Kenny. Something more than just friendship. It was as if his head was completely empty during that short trip and he just acted on instinct... and instinct doesn't lie about what it wants.

He felt like going back outside, putting his arms around Kenny and never letting go, but he wasn't going to. He couldn't. His mind may have been gone for the five minutes it took to get home, but now it was firmly in place, telling him to focus on Kevin and nothing else. He was sure that Kevin was connected to Kenny's obsession with Stan and, if he had feelings for him, he should try to help. Even if he didn't, he still wanted to know the truth.

Sheila: Kyle!

"Jesus fucking Christ, mom. Ever heard of lowering your voice when people are thinking?"

Kyle: Sorry, mom.
Sheila: Sorry? Why didn't you tell me you were planning on sleeping over at a friend's house?

"Mom, lower your goddamn voice!"

Kyle: It wasn't like I planned on it; it just happened.

Kyle's mom raised one of her eyebrows in disbelief and it looked like she was about to yell at him again, but she just shut her eyes, breathed deeply and told him not to do it again. Kyle understood this as "Go up into your fucking room before I tear your head off", so he did just that and focused on how to find Kevin.

"Alright, let's see now... Kevin's parents and his sister were lying about him running away. I can't talk to Butters because he doesn't know anything and neither does Cartman. I'm guessing that my only option really is to talk to Kenny... But I can't do it today. Mom will kill me."

Kyle spent the rest of the day in his room, trying not to piss off his mom.

Kenny woke up in the middle of the night after a particularly weird dream. It was nearly gone just as soon as he woke up, except for a vague notion that Kevin was involved and that they were talking about what had happened six years ago. He assumed it was just another nightmare, and he was glad that he couldn't remember it, but something didn't feel right. He didn't feel like he just had a nightmare. He was sad, but he wasn't scared or self-destructive.
Unfortunately, the more he tried to remember, the more it slipped away, until even the notion that Kevin was involved vanished, and all that was left was the hazy memory that he talked about what had happened six years ago. Because of that memory, Kenny started remembering what happened, pressed his face against his pillow and cried.

However, because of this memory, he decided he wanted to go see Kevin's grave again.

After what happened yesterday, Kyle decided to go talk to Kenny directly, but when he saw Kenny leaving, he followed him, without really thinking of a reason to do so. When they arrived at the cemetery, Kyle didn't even consider the possibility that Kevin could be dead and just figured that Kenny had a part-time job or something like that. However, when Kenny started crying in front of a grave, he realized the truth. He approached Kenny with great caution and put his arms around him. At first, Kenny didn't know who it was and, although he was startled by the sudden gesture, it made him feel better, so he didn't even try to stop it.

Kyle: ...Why didn't you tell me?

"...God dammit, Kyle..."

Kenny: ...You weren't supposed to know.
Kyle: ...What happened to him?

Kenny couldn't hold it any longer and just told Kyle everything. What happened to Kevin, who did it, why he did it and Kenny's role in all of it. When he finished, he started crying even harder, but Kyle just kept his arms around him the whole time.

?: It's not your fault...
Kenny: What?
Kyle: I said it's not your fault... You need to start... moving on. You've been stuck with your guilt for six years; you've suffered enough, even though you didn't deserve it.
Kenny: How can you say that?
Kyle: ...If it was your fault, I'd blame you for what happened. I don't.
Kenny: ...You don't?
Kyle: I don't. Stan got himself into trouble because of his own choices. You didn't do anything wrong.
Kenny: ...Thank you...
Kyle: I should be the one to apologize.
Kenny: For what?

Kyle finally realized that he had been jealous of Butters this whole time, because of how close he got to Kenny. After explaining it to him, Kyle also started crying and pulled Kenny in closer. The boys hugged each other for what seemed like forever until Kyle decided to do something he thought he shouldn't. Hesitantly, he asked Kenny if he was going to the prom with anyone. Kenny told him the truth, after which Kyle clenched his fists, closed his eyes and just blurted it out.

Kyle: Kenny, will you go to the prom with me?

At first, Kenny didn't know what to say. He wanted to say yes; he wanted to say everything he felt for Kyle, but he was too nervous. Everything was happening too quickly. First they were talking about his brother, then Kyle's jealousy and now this. His heart was pounding against his chest, and there was sweat pouring down his face, some of it mixing with his tears.
Kyle's ear was pushed against the taller boy's chest in such a way that he could hear his heart beat. He mistook the pounding in his chest for anger, which frightened him.

"I shouldn't have done that..."

Kyle: ...I'm sorry. It's OK. I shouldn't have expected you to say yes.
Kenny: ...I didn't say "no". It's just that... this is kind of sudden.
Kyle: Um... Well, I'll be waiting for you in front of the school. When you... make up your mind, meet me there, alright?
Kenny: ...Sure.

Kyle had been standing outside for almost an hour now, but Kenny was nowhere to be seen. However, since he had arrived almost half an hour before the prom started, he was going to wait a bit more. Eventually, Kenny arrived, carrying a small box.

Kenny: I'm so sorry, I was... getting this for you... It was custom made, so it took a while... Sorry.

Kenny opened the small box and inside there was a necklace with a small gold colored heart attached.

Kenny: See, you open it like this...

Kenny showed Kyle how to open the small gold heart, which had two spaces for pictures on either side.

Kyle: ...Thanks, Kenny. This almost makes up for you being late.
Kenny: Almost? What can I do to make it up to you?
Kyle: I dunno, but don't worry. I'll think of something.
Kenny: Are you sure you wanna do this? You know that they're going to do something stupid, right?

Kyle grabbed Kenny's hand, interlocking his fingers with Kenny's. Kenny was still a bit nervous from the idea of going to the prom with Kyle, but he also trusted him more than anyone else. He just wanted to make sure Kyle wasn't having second thoughts.

Kyle: I'm sure. I don't care what they say. All that I know is that you need to start moving on and that I like you.

Kenny and Kyle went inside, hands held. They didn't care what anyone else thought of them; they just wanted to be with each other. And they finally had their wish.

Yeah, kinda lame ending, I know. The epilogue will be uploaded in a few hours.