Like I said this issue was never resolved and she never forgave you, the simple fact is she has used this and will continue to use this against you. If that is the only reason for her insecurity then she will doubt anyone she ever dates.I apologized profusely for it, and she forgave me. This was about 3 months before the engagement. However, there remains a lingering insecurity within her mind about me and whether I will cheat.
Her insecurities are not rooted in what has happened in your relationship but rather her past.It's compounded by the fact that 7 years ago her parents went through a bitter divorce. In short, she told me that she saw a lot of her parents in us in the way we disagreed and also in our general approaches.
This says trouble all over it. You see I once had this type of relationship when I was young. We went on again off again so many times all it did was hurt me more every time we broke up again. Finally I just stopped seeing her, answering her calls or speaking to her until she could accept that we could only be friends from there on out and nothing more because having one thing being used over and over as a reason to break up wasn't fair to me. In the end she decided that she couldn't just be friends and broke off completely which was fine. The point is you are setting yourself up to fail again for the same reasons because of her insecurity and the fact she will use that one time again and again.She said she's not happy with me because she feels she can't contribute to the relationship, but unhappy away from me because she misses me.