My partner has had an affair but blames me rather than accepting any responsibility

Dilemma
I have just found out that my partner of 13 years has been having an affair. We have children aged three and five. I am devastated. He has moved out at my request and we have had counselling. He says he has been deeply unhappy for two years, that I made him feel undervalued and put down. I know he has been unhappy, but when I asked, he always said he was fine. I am prepared to change to try to build a new relationship, for the kids as much as for me, but he just goes on about how unhappy he was and what an awful person I am. I think there are other issues, as his dad left for someone else when he was 16 – which makes it more unbelievable he would do this to his kids. I can’t see a way forward unless he accepts responsibility. Or should I cut my losses and make the separation permanent?
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Do you feel sorry for this lady? Any advice for her?