They aren’t together but Henry just gets so fucking desperate and he knows Alex hasn’t been with anyone else because of law school constantly taking up his time. He goes up to him one night after getting off already and still not being satisfied. He begs him to fuck him and to make him feel it and Alex’s jaw drops. “What?”
“I need it. I need you to fuck me. It’s not enough, Alex, please”
And Alex can’t say no to his best friend (who he’s madly in love with) so he does. He lays him out on the bed and eats him out till he’s screaming first, though, because if this is his only chance to have Henry, he’s gonna make it fucking count. Henry is dripping and squirming by the time he’s cum again, but he outright yells when Alex finally slides in, his legs wrapping around his waist and grinding back against his dick like a whore (which Alex ever so kindly points out)

It becomes a regular thing, and they eventually realize that neither of them are only in it for the sex