It's one thing to feel like you should have been able to prevent your parents' divorce. Like that was your function in the family - to hold it together. Yes, as an adult I believed that: children are not the only ones who feel that way. When parents let kids into their problems and the children do actually seem to have some fresh understanding that sprouts even small successes, things become very entangled very quickly.
It's another thing to be the one that discovered and exposed the thing that ended it, to go with your sense of moral duty, even when it defeats the purpose you believed you were serving.
It's another thing then, to hear from your cheating father that it's your actions that have ruined your family, that have cost him his job and threatened your family's financial security.
It's another to be told by your mother, 3 years later, that you could have saved your family but apparently you just didn't want to. I was 29 and a mother of two, and my mom asked me to give my dad an ultimatum before he married his 3rd wife - "Choose me or her." She was sure that he would have chosen me. I refused. Looking back, it's the most unfair thing that anyone's ever said to me.
And it's another that she's brought up my refusal since then, and when I finally told her how hurt I felt from her request, she stood by it.