@The-one,
The-one,
I have been in a very similar situation. When my fiancee and I first started going out as a couple (we had been friends for a year prior to that), we lived about an hour and a half away from each other, and I was still in college. Well, I had many female friends in college, and I made the mistake of telling my girlfriend that I was having feelings for one of them. I hung out with this other girl a lot. Nothing happened between us, but my actions created the appearance that we were up to no good, and that's how my girlfriend interpreted it.
Now I'm engaged to that girlfriend, and I have entirely broken off communication with this other girl. It was extremely hard for me to do, since we were good friends, but ultimately my fiancee comes first. It very much pains me to know that I have instilled distrust into my fiancee's mind, but our relationship is so good together that we are both able to live with the pain I caused. However, part of our relationship has been focused on overcoming that pain, and we both make conscious efforts to move past it.
Trust me, the only way a couple can make it together after a cheating incident (and yes, cheating is wrong) is if both of them are willing to cooperate in getting past it. To me, it doesn't sound like either of you two are willing to do that. You sound resentful, and she is possessive. Believe me, I had alot of resentment too, and my fiancee was very possessive, but we have both learned to let go (not entirely letting go, but mostly).
Based on what you wrote, I do not think that you have accepted your girlfriend's faults like you say you have. More importantly, I do not believe you have accepted your girlfriend's good qualities either. Much of the time, when a man cheats on a woman, he tries extra hard to prove to himself that it is somehow her fault. It makes him angry that she isn't the one who cheated. It makes him agree that she's the good one, and he tries to find fault with her wherever he can. He will even try to find fault in the woman's good qualities. Believe me, at first, I was angry at my fiancee for willing to continue our relationship despite the fact that I hurt her so much. I thought she had some sort of God complex.
I think this is what is going on with you. You turn her possessiveness, which is a perfectly understandable reaction to infidelity, into some sort of fault, and you are looking to blame her for the problems in your relationship when you were the one who caused those problems. You need to accept the fact that the problems in your relationship are your fault, not hers. That is the first step. If you cannot make that step, then you will forever resent her, and you should break up as soon as you possibly can.