K-r-e-v-y-e-t-k-a
You don't really give a s**t about this guy, OP. You just want to hang out, have fun, and enjoy the rest of highschool before you leave for college. That's perfectly acceptable, but you can also do that with your other friends and perhaps another casual love interest.
This guy obviously can't take this "I enjoy your company" thing you two have. He wants more, he's lonely, and he's depressed and wants a commitment from
anyone because of that. He's... actually going to be your "downer" the closer to august it gets. If you want what's best for both of you, you should break up with him for the cheating -- let him know that it's not okay, ever -- and continue to enjoy your time in your home city. You should also let him get a chance with his overly zealous friend; perhaps they would be a better match. If you do this: you'll have a clean history of never forgiving cheating, he'll get his shot at "love," and you'll have a clean emotional slate for college. Everyone wins. Just never have pity sex with the guy after you two break up.
Yeah, I guess I don't give that much of a s**t about him, but I still like him. The thing is, I feel like he may be able to handle the "I enjoy your company" thing now that he doesn't have to pretend he doesn't like me as much as he does, and even if I break up with him, he has no interest in his friend (according to him, it was only ever about me, and he isn't even attracted to her) and can't stand to see her because it reminds him of what he did, so he's cutting off his friendship with her forever. But having a clean slate of never forgiving cheating is probably a good idea, too.