“We shouldn’t have done this…"
That’s what Stiles should say. He should set the record straight, make it obvious the whole thing was a mistake (hooking up with your best friend when you’re in love with him and he had no idea? Yeah, it falls under one of the worst mistakes of Stiles’ life, honestly.) This whole thing consists of choices Stiles should have made. And didn’t.
And still doesn’t. Because he takes one look at Scott in his bed in the morning, sleepy, shirtless, hair messy, and his heart jumps in something bittersweet. Stiles knows this is what he’s missing. That this is what he wants and can’t have, and Scott…does Scott realize any of that? Or was what they did just some kind of mix of in-the-moment pity and hormones? Does he have any clue how far beyond that it was for Stiles?
It’s better to pretend it never happened. That their friendship isn’t completely ruined and everything’s normal. So Stiles shakes Scott gently awake like he would after any other night, barely takes the time to say "school”, and then he’s getting out of bed and busying himself with getting dressed. He doesn’t look at Scott at all as he grabs a shirt and pulls it on.