I agree with DH that a professional might be able to help. Breaking down years of resentment is difficult, but can be done. for me it really helped to voice the resentment in front of a third party. She was able to help me vocalize why it still hurt so much after so many years. I had tried before and actually thought I was past it, but it still reared its ugly head. I think my husband was also much more willing to truly listen while we were sitting in front of the marriage counselor.
It's easier to NOT have those walls with someone new. So don't lose hope, if you both want your marriage to survive, this can be fixed.