Most Helpful Guy
Sex bonds us to someone... Sometimes forever.
That is why it is important not to introduce it into a relationship until the time is right (Honeymoon).
Unfortunately you are bonded to an unworthy guy. He is unfaithful.
You must severe those emotional ties with him, or get caught up with him again, and feel the feelings of hurt will be twice as bad next time leaving you feeling twice as empty, emotionally.
Most Helpful Girl
I think he still loves and cares for you. Obviously you both are still emotionally connected. There are two paths for this to go. You need to do whatever you can to break it off with him. He cheated on you. You should respect yourself to know that you don't deserve that. You need to cut off all communication with him and go on a cleanse from him. Maybe not meet new people, but hang out with your girls, travel, go do fun things and focus on getting better for you. Workout and exercise, try new things, focus on making yourself better and create distance between you two. Avoid the temptation to contact him. You need to focus on you and moving on from this. You deserve better, and a new person who won't cheat on you or hurt you. That's not healthy. Then later on after a several months, you can bring him back into your life as friends at least.
Other path, you can try and make it work with him. But you need to work with him and commit to that's what your decision is. If you want him, have a discussion with him. You need to know exactly why he cheated on you and what his reasons are. You have got to know all the details to then decide if you really want this guy back. Good guys can make bad decisions. You need to figure out if you can live with yourself if you stay with him after all he's done to you/for you. If you decide to stay with him, try and talk stuff out to him. Both of you need to put your feelings out in the open to know where each other stands. Then decide if you can move forward together and put this behind you.
No matter what you do, you need to commit to one or the other. Being in the middle like this isn't healthy for you either of you and it isn't any fun to waste energy like this. Having it in the middle like this is too painful I'm sure, and you're missing out on new experiences, having fun, and a new you or building a new a relationship and perhaps future with this guy. What do you want? Pick one or the other. And do it.