Personally I would stay on the high moral ground. As you don't agree on what H and OW is doing (having an A) and being selfish, I would not act the same way. Having said that, there is no need for you to feel miserable and be a doormat (which I know you are not!!!) This is tough. I persaonlly also would not contact OW as in my mind, she is not even worth my paying attention to. I really don't know what I would do in this situation. May be sit down with H and states that since "we are staying in the same house in this odd situation as housemates/co-parents, let's lay down some rules about how we behave?" Not sure as I can sense that H will not follow the rules. How dare him still initiate sex with you while proceeding with D? That's cheating on OW , ha ha.
LO, take care and stay sane. Obviously your H is not.
