I feel really guilty about what i did?

Woah. This guy called you a slut? Honey, you are NOT a slut. I don't care who called you a slut, you aren't. I can see what you are going through because last summer I was in the saaaaame situation. It's almost scary how similar it is. Anyway, the best thing you can do right now is recognize how you feel and plan steps to keep this from occuring again until you can do what you want to do without feeling this way. Just take it one step at a time. If you like this guy, tell him and tell him that is why u can't keep doing this. It seems like he has some feelings for you too, unless he's the one who called u a slut, then I'd just say eff him. But, if yoo like him hun, you should go for it. Atleast try. And if he says no, don't keep giving up your body to someone who won't respect it.