It sounds like perhaps this guy is embarrassed to find himself in a situation where he fooled around with someone whose emotions and feelings he doesn't want to deal with afterwards. This just shows he is probably not worthy of your time and affection. Instead of talking with you about what the two of you have done together, he may think it is easier just to call you names and make himself look better.

If you want to change things, there are several ways you can try.

You could ask him directly why he is saying these things about you. You could ask him if he thinks he is a whore and a slut, because he did the same things that you did.

You could go through his sister to find out what is going on. This might be easier than asking him, but it involves a third party and might make things even more messy. Or you could just ignore him until this passes.

If you decide to put this behind you and move on, think about what you liked about your connection with him and how you could find that quality in another guy who is much cooler.

Your sex life is your own business, although gossip often spreads about what people are rumored to have done. If you don't feel good about the circumstances under which you fooled around with another person, you may be even more concerned about what other people think than if it was a satisfying connection.

Also, if you get involved with someone in the future, it's a good idea to talk about what is going on and to make sure you're both comfortable with it. That way, you can avoid a similar situation in the future.

You can also check out another Help Me Heather advice on this topic. There's a lot to think about regarding the ridiculous double standard regarding sex and females versus sex and males.