Well I should clarify, that when I separated from my husband, I was not in the midst of an affair, so there was no other person to get the kids mixed up with. And in my case, I think my leaving him sent my ex-h into a sort of tail-spin MLC...and what happened as a result of that was that HE walked away from our son. That was an unexpected development, for sure!
Even at my foggiest, I did not put my affair ahead of my kids. So maybe I am not a good voice for people who do like what your H is doing. It just doesn't resonate with me at all on any level.
Which is not to say I am a more moral person than anyone else. Just that for whatever reason, thankfully I was spared of the type of fog that causes people to abandon their children.
My kids were 14 and 19 when we separated. The 19 year old was on her on in college. The 14 year old is the one my ex-h abandoned in the midst of our separation. It was as if our son looked too much like me and my ex-h didn't want to even see his face. I'm just speculating based on what it felt like, not on anything my ex-h said.
IMO, if a parent is going to leave the marriage and immediately introduce a new partner to their children, then they are really F-ing things up! Can I ask, is your H a child of divorce himself? The reason I ask this is that it seems from what I have seen and gone through, that adult children of divorce are more sensitive to their own children if they come to a divorce themselves. But adult children whose parents were never divorced don't seem to "get" what dragging a child through this stuff does.
I could write for pages on my opinions about the children going through these circumstances...my heart goes out to you and I hope somehow he will get some sense into his head. Again, were his parents divorced?