How long ago did this happen?
How has he acted since then?
How old are the two of you?
Where did you meet?
Who initiated the intimacy?
I've seen it go both ways. Of course I always suggest against it, because the majority of the time it doesn't work out. Mainly the guy is thinking "if she slept with me on the 1st/2nd/3rd date, then maybe she sleeps with every guy she meets this soon".
I find that many guys are thinking this way less often, maybe because sex and sexuality is so much more commonplace and accepted openly nowadays. I find that a lot less guys are taking this offensively, but they tend to be in their 20's.
I would say take it slow. There's no way to take it back, but you can let him know that you think the two of you may have moved too fast, and ask him how he feels about it. The botXXXXX XXXXXne is he's either interested in a long term relationship or he's not. Secondary, he's either interested in one with you or he's not. Don't stress, stay calm and be yourself. Maybe you'll want to hold off on sleeping together again until you can get to know each other better, maybe he;ll agree to that, maybe he'll think you're nuts. Maybe you feel like, hey what's done is done, and continue to sleep with him, and that's ok too because it's all about choice.
You made a choice, now you have to see it through, good or bad. There's no sense in worrying too much about it because you can't change what's happened already, you can only affect what happens in your future.
I welcome your thoughts, let me know if you want to talk more.
I would probably ask him how he felt about it. "Do you think we moved to fast?", "Do you think we should have waited a little longer?". Asking if he thinks less of you won't matter because if he has any brains of course he'll say no, besides it brings up too much of the negative.
Don't dwell on it, bring it up, see what his response is and respond accordingly. Remember, if it's meant to work out, it will. Be yourself.
I'm always here if you want to talk more.