Relationships- The Fins Of Our Existence

Dear Coach, I am in a relationship that is currently three-years-old. I love my girlfriend so much and I have plans to marry her but unfortunately, she is so difficult to deal with. ​​​​​​​I am the one who is always understanding and bend in order to sustain peace in the relationship. A couple of months ago, I found out that she was cheating on me with her ex- boyfriend and when I confronted her with the issue she confessed that it was true. I forgave her then we moved on with our lives. Some time ago, I was caught having a meek conversation with my ex- girlfriend and she got so mad that she took all her belongings in my house and promised to never come back to me. Regardless of the many times I have asked for her forgiveness, she seems not to be accessible. She really has built a hard wall around herself and it pains me that she cannot accept my apology. What should I do Coach so that she forgives me and things go back to normal? How do I assist her with dealing with her unforgiving character?Yours, Anonymous