I too had and still struggle with resentment towards my exA. He and I have not spoken in a long time, but he rears his head in my life semi-frequently.
In my mind, the man owes me a HUGE apology for lying to our friends, my family and me. His lies damaged my relationships with other people. I think at this point everyone pretty much sees him for what he is, but so much time has past and so many lies were told that t just is what it is. He kept a bunch of my things which still bothers me. I have long since given up thinking that I will get them back, but the total lack for respect from him given the cheating and lying too. Why keep my stuff? No boundaries. Everything is about him and his needs/wants/emotions. Others are secondary if they are even relevant to him. Major self absorbtion. My last resentful area with him is that he told me that he would help pay for me to go back to school. I was working full time and unable to return to school. He told me not to worry about the expense and that he would take care of it. Nothing was ever in writing. He left me 6 months before I graduated when the loans were coming due. He knew I had NO money at the time and needed his support. That was our agreement. HE came up with the idea and I kept going back and forth about what if something happens. He assured me that he would take care of things regardless what happens. The economy plummeted, I could not find work and had NO place to live. He knew these things and could have cared less. Devoted girlfriend, fiance, best friend and it didn't stop him from walking away on commitments to me. That hurt.
Now, I see how sick he is and that I was naive for believeing him. I used to think that if you talk it out and people make promises, then it means something. Like a contract that you have to follow. It doesn't.