I don't own Teen Wolf and never will. No copyright infringement intended.
Stiles gaped in horror at the scene in front of him and struggled to comprehend it. "My eyes! My eyes! What the fuck did I just walk in on?"
"Language," admonished John. He actually had no ground to stand on, but he was still a parent.
Meanwhile, Melissa scrambled to find her clothes but just ended up putting on John's shirt since hers were scattered all over the place. "You weren't supposed to be home until later!"
Stiles glared at them both. "Don't turn this around on me! You're the ones having sex on the couch. We sit there! Why wouldn't you fuck in a bed like normal people? How long has this been going on?" He had so many questions and he wasn't sure he wanted the answers to them right now.
"Trahaearn Caerwyn Stilinski! I am your father and you will not speak to either of us that way. I don't care how old you are – You will respect both of us. We are adults and the door was locked. We can make love wherever we want."
He cocked his head at that. "First of all, rude at the full name, John Kevin Stilinski." Off his father's glare, Stiles apologized before continuing. "Second of all, make love? Are you two in love?" Because he could handle this if it was love.
Melissa nodded. "Stiles, your father and I love each other very much. We were waiting to tell you once we knew where this was going."
John continued for her. "But we both know where this is going. We're in it for the long haul, kid."
Melissa beamed at him and then leaned her head on his shoulder. John pulled her closer and then kissed the top of her head. "We're really happy. We don't want either of you boys to be upset about this because your happiness matters to us. So let us tell Scott, okay?"
He nodded. "As long as you're happy, I am. But I need to go and get brain bleach to scrub those images out of my mind forever." Stiles waved goodbye and then bolted the fuck out of the house as fast as he could. He and Scott had joked about the possibility of their parents sometimes, especially once his dad found out the truth, but they had never expected this to happen. He wondered if they were going to get married someday until realizing he was getting ahead of himself. Stiles wasn't surprised when he realized he was at Derek's. They had started getting closer after Boyd was murdered by the Alphas.
Derek was reading a book when Stiles strolled in. "Do I have to give up on you knocking?" He didn't mind too much, though.
"Duh. Do you even know me?"
"So, what's up? I don't think anything is really going on right now." Derek couldn't help the plunge into worry and was suddenly paranoid he had missed something new that was attacking Beacon Hills.
"Nothing. Promise you won't tell anyone what I'm about to tell you?"
Derek nodded. "What is it?"
"I just caught my dad and Melissa McCall having sex. On our couch."
"Is that is? I've known for weeks now."
Stiles sputtered. "And you didn't tell me? This is important information that I should have known before I walked in on it! Damn it, Derek."
Derek just laughed. "I figured they'd tell you and Scott when they were ready to. That they wanted to keep it private. That's it. How are you doing with this?"
Stiles shrugged. "It threw me for a fucking loop, I'll tell you that. But Scott and I have been joking about this for years. And they both deserve happiness so it's okay with me. I just need to get those images out of my head because I can't deal with this trauma anymore!"
He snickered. "I walked in on my parents once. They locked the door, but I was an impatient twelve year old and forced it open. Never did that again." Besides Cora (and occasionally, Peter, when the man wouldn't shut up about them), Stiles was the only person Derek was able to talk to about his family. It hurt him too much, that reminder of what he had once had. He trusted Stiles, however. And Stiles occasionally talked to him about his mom, although it was rarer than Derek talking about his parents and other family members.
"Well, at least we can share that trauma together."
And that's when Derek suddenly decided to be brave. "I know a way I can take your mind off what happened."
"Oh yeah? What's that?" Stiles was curious and hoping it was what he thought it was. But maybe he was holding out too much hope for Derek to finally catch a clue.
Derek stood up and then slowly approached him. After a brief moment of indecision, he kissed Stiles. After a few seconds of shock, Stiles broke out into a smile and returned the kiss. "I like this way of taking my mind off what I saw. We should do this some more."
"I agree." Derek was terrified of all the ways this could be wrong, but he wasn't going to let his fear dictate his actions right now. He wanted to be happy and selfish right now. He had the right to be happy for just a little while.
After they finished making out, Stiles and Derek sat down to watch a movie together, one of the few they actually agreed on. This was the start of their relationship, even though neither knew it. And for now, they weren't going to let their insecurities ruin anything (they'd pop up later, leading to a few fights, however).
The next day, Melissa and John came clean to Scott, who had suspected the truth for weeks now (Stiles proceeded to complain that no one ever told him anything, upon which John guilt tripped about werewolves). A full-fledged relationship started once everything was out in the open.
"I feel like I can be truly happy for the first time since Sorcha died," John told Melissa one day over dinner, right before they were about to be descended upon by several werewolves and human teenagers.
Melissa couldn't help her smile. "I'm glad I can be that person for you, John. And I feel the same way about you." She looked forward to their future.
Derek and Stiles held hands under the table and just enjoyed themselves that night. They were surrounded by their family and life couldn't get any better.
No one was aware of the monster lurking, getting ready to strike Beacon Hills. It would be their last stress-free day for a long time.