Most Helpful Guy
1. If he wanted you, you would have heard from him.
2. You shouldn't have had sex with him, you shouldn't have hung out "as friends" (that is b. s., as you knew what you were doing,) you shouldn't have had any contact with him.
3. He was unfaithful to his current girlfriend. If he reunited with you, wouldn't you be concerned about him being unfaithful to you?
4. The only sane thing to do is to stop ALL contact immediately and wait until you start feeling a bit better. Remember, you did this to yourself and you need to learn from this experience.
Most Helpful Girl
First of all I've been in your situation before. It's hard. You're still in love with this guy and he suddenly wants to hangout with you, and your normal judgment of the situation goes right out the window because the person who you're crazy about wants to see you. Scientifically speaking, you screwed yourself over because when women have sex with a guy, we release oxytocin, a hormone that actually creates a stronger bond between you and the person you're sleeping with. So your body thinks you have this connection with this guy and you feel more in love with him when he really just used you. The only thing you can do from this point on is just to move on and break contact. I never got over my ex until I finally stopped talking to him for good. Don't call him or text him, don't stalk his Facebook, and don't respond back if he writes you or calls you. Better yet just delete him off Facebook and delete his number so you won't see his posts and you won't be tempted to send him a text or a call.
The next thing you should do, is have a girls night with your friends. Go do something fun that will help take your mind off what happened. Fix up really nice and try to go somewhere social and if you can flirt with some guys do it. It will make you feel better that someone else is noticing you. And lastly don't be too hard on yourself. Everyone makes mistakes. Just don't make this mistake again. :)