I'm curious about how it goes the first time they have sex in the ACT verse
In my opinion, badly. My friends, please go elsewhere if you want to imagine that the sex is nice and not embarrassing.
Harry just wants sex, but mostly so he can be as close as possible and touch as much as possible. Like, it doesn’t have to be fancy; he just wants to be touched. He tries to do this with Draco, but Draco is nervous out of his mind, and wants everything to be perfect, so he keeps trying to be new and interesting and different, teasing Harry and demanding these things while thinking it’s just to pleasure Harry. Harry really just wants to be touched, so he’s okay with these things because Draco is still there with him and touching him and they get to be naked, but he’s really pretty frustrated. But he doesn’t want to take over or tell Draco he’s doing it wrong because. Well. Anything Draco does to him still feels good, and Harry isn’t used to expressing that he wants to be touched and cuddled, so he can’t think of the words to ask for what he wants.
Meanwhile, Draco is so nervous that he uh, goes off too soon, and in fact continues to have problems with premature ejaculation for like, the first year or so that they’re together. It doesn’t bother Harry, but Draco is absolutely mortified, and makes potions to fix it, which have the opposite effect, and Harry tells him to cut it out.
I mean. Harry thinks it’s fine, in the end, because it’s Draco and Draco spoons him afterward, and Draco is upset about it but Very Determined not to be a mess next time (he fails). But while it’s nothing either of them fantasized about, they’re really happy to be touching each other, and Harry tells Draco more than once that it’s not their last chance; they’ll do it again very, very soon. So it’s fine, but doesn’t really become a strong point in their relationship until much later.
Does that answer your question, or did you want more detail?