While I know that this is probably never going to happen in canon, it's fun to always imagine how it could happen. I'm pretty sure Kurapika would tell Leorio first about his problems because he's probably the closest person his age that he's already been through a lot with (the Hunter Exam) so it seems like a natural choice for this to happen.
Please enjoy!
Kurapika came out from his room rubbing his eyes. The past two weeks had drained him. He couldn't remember the last time he slept soundly that month and all the extra research for personal reasons were starting to catch up.
Looking up at the clock on the wall he saw that it was already 11:35 at night, successfully leaving him only a few minutes left in the day to attempt to go to sleep. He oh so badly wanted to stop and do nothing but stare at the ceiling, but if he stopped, he would be plagued with images and words from that man...
"Kurapika, why are you still awake?"
Kurapika almost jumped, the voice startling him as he looked over to see Leorio.
"I should be asking you the same." He said, offering a tired smile to his friend.
Leorio smiled back, making his way over the Kurapika, book in hand.
"I wanted to return this," Leorio began to explain, tapping the novel on top of the blonde's head. "It was interesting! I especially liked the ending part where the archer guy found out his past!"
"You read the book and still don't know the character's name?" Kurapika laughed, glad for the distraction he was graciously being given.
Leorio just grinned sheepishly and shrugged, pushing the book into the other's hands.
"So what's been weighing on your mind? You've been doing more research lately and you look really tired too. It couldn't possibly be work since you usually finish that pretty quickly, so if it's anything I could, oi Kurapika, are you okay?"
Kurapika had felt his body begin to shake, the all nighters he had pulled for the past two nights were finally taking their toll on him. His head was also beginning to be filled with visions of that wretched man again, and finally he could take his hallucinations no longer.
"Leorio, we need to talk."
Leorio looked surprised, but agreed to it immediately, concerned for his friend's well being.
"Sure, whatever you need to talk about, I'll listen to it."
Kurapika nodded and lead him through the common area and out to the balcony, where the fresh air greeted the blonde and his companion.
Leorio took a seat on one of the chairs that was set out there and Kurapika did the same, folding his hands and putting them in front of his face, almost like he was ashamed of what he was gonna talk about.
And he was.
"Leorio I... I think I love someone." Kurapika started off, staring out to the city lights below them, car horns blaring every now and then. "They're a bad person and their morals are so far off base, but I can't help but feel the way I feel for them..."
The Leorio look surprised at the news but smiled anyways, trying to be optimistic about what Kurapika was trying to convey.
"Oh come on Kurapika, whoever you like is surely to be a good person! You wouldn't have it any other way!"
"I know Leorio! But that's the problem, they're not a good person! They've done so much harm to this world and yet..." Kurapika faltered off, looking down at his hands once more as if they would give him the words he was looking for.
"Kurapika, listen, it can't be that bad, and if it is, so what? No matter what happens, Gon, Killua, Melody, and I will support you. Heck, even Canary would support you! You know, that one Zoldyck butler?"
Kurapika allowed himself to smile a little, thankful for Leorio's comforting words.
"Even if you say that you can't be sure-"
"Kurapika I told you, no matter who you love we will all accept you and support you with that relat-"
"I love Chrollo Lucilfer!"
There was a stunned silence before Leorio sputtered out a cough and gave Kurapika an incredulous look.
"Chrollo? The one in charge of the Phantom Troupe? The ones you have sworn to destroy?"
Kurapika only nodded, a knot in his stomach forming again at the thought of the Spider head.
"Are you sure you're not mistaking it for an over boiled type of hate? That you hate him so much that the emotion is basically raw enough to feel nothing?"
"I don't think that's the case Leorio, and if it was, I would know."
Leorio looked down at his companion, his hunched over figure almost sad.
"I was frightened when I first discovered that I didn't hate him." Kurapika sighed, looking out towards the city lights. "I couldn't describe it to anyone close without seeming crazy, so I went around and asked random people what it was I was feeling. They told me I was in love. I couldn't take their word for it so I looked it up, thinking it might be symptoms for something else, anything else, and as time went on, I kept getting the same results. My feelings for him, in the meantime, had only gotten worse, to the point where I felt like hunting him down personally and confronting him about what I was feeling, but I could never..."
Leorio nodded, knowing all too well where his friend's thoughts were going.
"Well come on Kurapika, it's not like you've masturbated over the thought of him right?" Leorio joked, trying to make light of the situation, "I mean that would definitely... oh God you didn't..."
Kurapika's face was blushing immensely by the time Leorio had looked over at him and he turned his face away from his friend, coughing to cover up his embarrassment.
"A-anyway, through my research, all the results I had received told me that what I was feeling was lead by a chemical reaction of dopamine, which is-"
"The happy chemical." Leorio completed, knowledge from his medical books flooding back to his head, every indicator telling him that what his friend was feeling was genuine.
He stared at his friend for a while before patting the Kurta on the shoulder, shocking him.
"Well, even if that's how you feel about your enemy, who are we to judge? Just make sure that that's what's going to make you happy okay?"
Kurapika gave Leorio an empty look before he smiled warmly, nodding his head.
"Of course. Thank you for letting me talk to you about this Leorio."
"It's no problem! But if that jerk does anything as so much insult you he'll have to answer to us okay?"
Kurapika laughed, hitting Leorio lightly on the shoulder.
"Yeah yeah, I'd like to see you try and punch him like you did Ging!"