Negative relationship with children's father

He told me I have a negative attitude towards him, and he's right. I try to hold everything together for our 2 kids but he has hurt me alot. He had an affair before we had the kids that I forgave him for but the hurt never went away and despite all the work I did over that, it did taint my trust of him. And more so since having the kids he just never stepped up, I had a really hard time after the 2nd was born and he didn't support me. I barely slept, did everything the kids needed and he just lived his life. It's still the same now. So when he said that I have a negative attitude towards him, my gut wants to scream wtf do you expect. Instead I'm on here because I have no idea what to say that won't piss him off and start another argument.