Thanks, everyone.
I posted less than an hour after it happened, and was feeling very embarrassed and worried that I’d changed the dynamic of our friendship too much.
It wasn’t really brave or gutsy, it was a complete impulse (and a selfish one, at that) at the end of an otherwise great night. He walked me to my car, we hugged, I kissed his cheek, he kissed my cheek, and next thing I know cheeks aren’t involved anymore and I’m not being kissed back. (First time that’s happened, btw … I’m not bragging, it’s just that I’m not usually so impulsive and I typically only kiss men if I’m way more sure that they wouldn’t mind. Not being kissed back is a very weird feeling!) Then I apologized – twice – and got in my car and left.
I don’t even have “feelings” for him: I like him a lot, and we get along very well, but I think the most I’d want right now is a friends-with-benefits kind of thing. It’s definitely not unrequited love or anything – unrequited lust, at most. 
He’s supposed to come to my house Wednesday evening for poker, so sometime this weekend I’ll send him a quick e-mail apologizing again and saying that the last thing I want is for him to feel uncomfortable around me, and then I’ll see if he shows up for the game. He’s moving out of state in 2 weeks, and worst case I won’t see him again before he leaves … which would suck, but would be my own fault.