Geez I'm so sorry. What a complete bast@rd You're not doing yourself any favours? Good lord can he be any more narcissistic? I highly suspect if the tables were turned and he could actually have kept it in his pants and it was you that cheated, he'd be having some choice words with the man that ruined his marriage.
I think of my DH cheating on me and I feel physically sick. I can't imagine what you are going through ready to birth any time.
Move now while you still can.