How do I let the past go and move on?

[color=#FF0040][b]YES, it’s long, but I really need some advice:[/b][/color] I have been married for almost 3 years. I have known my husband about 9 years, but we dated on and off…more OFF than on and to add to that, were were long-distant. During our OFF-time he got into another serious relationship, but always had me on the mind and in the heart. This caused some trouble in his relationship, as he expressed his feelings for me to her…so, they eventually broke-up. So, we find our ways back to each other after not talking for a long while and decide that we really want to move to the next level…marriage. Because of our long lapse since our last relationship, we both needed time to make sure that was what we wanted. So for a few months we never officially said we were “together” because I think he needed time to let HER go and I needed time to make sure this was going to work. A couple of months later he proposes and after asking if this was definitely the step he wanted to take, I accepted. After getting engaged and starting to make plans to marry in the next 4-6 months (because we didn’t want to wait a year or two) he admits that he has had sex with HER (after proposing). I forgive him because I wanted him as my husband and I felt like forgiving him would show that I had grown and matured. I later regretted this because it never left my mind. So, a few months later we get married and I move out-of-state to be with him. We started off rocky and we argued over a lot of things…some REAL issues, but mostly stupid things. We blamed it on the fact that we never were around each other longer than a week or so when we visited each other, so we really didn’t know what it was like to be with someone majority of the time. 6 months later I find out that he has communicated with his ex. I blew up and we had a really bad week. My trust was broken and on top of that my mom had just passed a few weeks prior…so it was a really emotional time for me. So, we eventually work through it, and he advises that he will not talk to her again. About 5-6 months later he leaves his email open and I discover emails that were written after he said that he would not talk to her again. I confront him and he says that its hard to stop talking to her because he truly cared for her and still wanted to be friends with her. I told him that because of the type of history they had, I couldn’t accept a friendship between them. So, after working through that he assures me that it won’t happen again. OKAY…last November a small disagreement turns into a HUGE HUGE argument and he begins to truly question our marriage and if we would ever work. He basically asks for time (and at the time he was away for work). He never called me and was extremely short and cold with me for about a week. He finally calls and tells me that he does not want a marriage with me any more…that so many things have built up and repeated themselves and he wasn’t sure if things would ever change. I’m devastated and plead with him to come home so that we can talk face-to-face. So after a hard weekend and hearing my side of things, he says that he wants to work on us. So, after a few weeks of anxiety and worry, things get better…we’re handling disagreements better, hearing each other out, communicating more, etc. So, now lets get down to it. A couple of weeks ago he leaves his email open and I look, lol, actually RESEARCH A.K.A SNOOP. This is a MAJOR no-no and I know this, but because of the history, I was just compelled to look and once I started looking it turned into digging. So, I dug and found several emails that were written to the same DANG ex during the time that he had me on Ig (ignore) when he needed “time”. To sum it up, his emails were basically his attempt to open the lines of communication with her because he was so sure that we were divorcing. In response to his initial email, she is hesitant and wants to know what prompted the reaching-out. HE doesn’t want to give details, but eventually she gives in and then comes the EMOTIONAL overflow from her and how she missed and loved him so much and how she always thought they were soul mates. Now his emails don’t go that much in detail, but they do express that he is happy they are connecting again. So, as a result of our long weekend of discussion, there is an email telling her that he “got his mind changed”, which made me feel like crap…like I CONVINCED him to WORK THINGS OUT WITH HIS WIFE!!!! So, he tells her and she is furious and hurt because she thought that this was finally her chance to “get back in”. There weren’t very many emails after that one and I honestly think that because of the interruption in communication, he was able to put work into us. ALRIGHT, so I confront him calmly and without anger (because I really wanted to handle it effectively and totally different from problems in the past). I admitted that I was wrong for looking, especially because he was never 100% comfortable with me seeing his emails, just because he felt like I wanted to look to find something bad and that showed that I didn’t trust him. I expressed that I was more so hurt by what I read and really suspicious. He advised that he was wrong for the communication, but that he knew it was a mistake and it is definitely in the past. HOW MANY TIMES HAVE I HEARD THIS? So, I forgive him because we have been doing very well and I trusted that he no longer communicates with her, and I wanted to move on….but by this time he is FURIOUS with me because I looked in his email once again and he made flipped it to make it seem like my wrong was worse than his. He didn’t want to forgive me because it was a repetitive thing that I knew he didn’t like but did it anyway. After a few days of distance, sleeping separately, avoiding eye contact and quality time before work with me, he tells me that he doesn’t know if he can let my actions go. I express that I think that both of us were wrong in our actions (past or present) and that I trust him and what prompted me to look in his emails had nothing to do with the past experiences with her because those things were really really not a threat to me and that I was glad that the last 6 months have been tons better. We eventually reconcile but I’m still thinking about everything and then things from the past start rushing in. So I start to feel stupid about forgiving him this time and in the past because of the repetition. I am truly tired of this Ex being a repetitive issue and find it hard to think that this time is different…but am trying so hard to believe that it is because I honor my marriage, want to show him that I trust him, and feel that I was on the way to finally healing from the past communications. Alright people, I need advice on how to let the past be the past and truly give my all to this man. The truth of the matter is, I have hurt him as well..I’m not trying to play innocent (but the hurt never involved another man), and we have addressed those things, but I never hurt him to the degree that he has hurt me. I am really trying to figure out if I am scarred to the point of not being able to forget the past or if I am just plain stupid for trying to keep my marriage. He has stated that he has not cheated sexually (and I believe him) and that the emotional connection was a mistake, but because he wants Us to work, he has honestly let that go. A part of me wants to leave…but a bigger part of me wants to move past this. The last few days have been crazy within my head. I have not been able to be at ease or peace, can’t sleep, and get kind of angry when I look at him. I’m just frekin confused and not sure if I made the right decision my forgiving him before PROCESSING the whole thing completely. PLEASE HELP!!!! (Sorry this was so long, but I felt that the details were needed for a better understanding.)