I can't recall... what is the status of your H and OW? Do they live together?
Either way, as an observer, it seems to me your H limits his exchanges with you to matters about your son. Every so often he will toss you a crumb and let you know something else (ex: family illness) but otherwise it is all about your child.
It seems he wants to be a good father and is trying to create a R with you that is mom/dad but has yet to make any effort in creating a man/woman R with you.
I am not trying to be ugly but it does seem you allow your H to cake eat. He has zero consequences for his actions.
I would go as dim as possible, drop the rope fully and put your focus on something else. Start showing him what a legal divorce will look like. Right now he has the best of both worlds IMO. You as the stable and great mom who is pleasant to her spouse and he has the OW who gets all the romance, fun, sex and intimate attention. I would remove myself from that equation (and yes, I had to do that as well with my H). Recently my H has been contacting me (we virtually have no contact) quite often with very nostalgic and loving messages. As long as he is living with OW he gets nothing from me ever again.
I will never be an OW to ANYBODY, even if the "anybody" happens to be my legal husband.
