I agree with Karen, ".....he made our situation worse in his mind back in Dec. when his pa started. He says b/c he was under stress, but I think it also helped him justify the pa."
It seems to be a common denominator in affairs to reach for all that would justify having it, & therefore it's pointless to defend yourself on any of the issues. In fact, I think it might have the effect of him digging his heels in & taking the focus off the real issue.
I just sent a link to your personal e-mail geared for the OW, but so helpful on seeing the big picture for all involved in the triangle.
I think you can show very strong & deliberate in other ways w/out responding to his statements. Sitting it out is the way to go I think.