What can I do?

Your case is a very strong one and ill do my best. See the way I see it, your still hurt because of the cheating, and in a way, to help the healing process you've made a false hope rise in your heart that this man will change and come to you. But the thing is that you know its not going to be this way cause he already showed you first hand that he can cheat on you, and now he showed you more because if he can cheat on you and cheat on another with you then he can cheat on anyone. No the real problem for you is that you wish for the pain to go away. Well I think your pain will go if you start letting go of the image of you and him together again. When you do this then the real healing starts, and as a bonus you say that you are not so wild for your new dude but the deal is that you'll never find another home in another heart if you don't close the doors to the one that hurt you. Hope it helps in any way. May God be with you.

I totally understand your situation.
From experience I would say wait it out, give it a few months, I know that sounds like a long time, but it will help you have a good indication of whether your love for him is real, or if its a mixture of unresolved issues/ or even jealousy.
I think you should let him know that you still have feelings for him, but that he wronged you seriously, and that you can not and will not just take him back.
I don't think once a cheater always a cheater is true, so there could be hope for him, but I would tell him that if he really wants you, then he would have no problem dumping his girlfriend for you, and waiting and behaving himself until you are convinced he is worth your time.
I mean some people, are all about the chase- hopefully that's not his issue. Just be honest with yourself . Think about what you really want, and what you need to keep you sane and happy and respected. Don't let him ever have the power in this situation.