I can relate to that! All my AH's past girlfriends were crazy b****es and they all cheated on him. And then as our relationship (and his drinking) progressed, I started to get accused of cheating on him, and I was called a crazy b**** (among other more hurtful names).
"You girls are all the same," he would say.
There were times I thought about contacting his ex gf's too. For me though, it wasn't to apologize, but because I wanted someone to commiserate with who I knew would know exactly what i was going through. I never did. Glad I didn't. Really glad.
I'm with Lexiecat on the letter writing