I am totally in the same boat as you. My H wants to be friends because he has no friends except OW, except OW is married still and for a while when he would talk to her about me (last summer and fall) all he did was complain about how bad of a friend she was because she wouldn't make time for him. H has completely pushed away all the friends he did have. Many of our mutual friends (specifically the guys) didn't want to here about what was going on because they wanted to be there for H, but now he has completely ignored them and won't talk to them at all.
I think he has a few old friends he has contacted, but they don't hang out much (and they only hang out as much as they do because I asked a few of them to help H out since he had no one and for a while was suicidal).
I just now decided enforce the boundary of not being friends with H (I told him when he first moved that if we Ded I would not be his friend so maybe a reason why he won't file...who knows), and it is hard. For me, H left and abandoned S and I. He sees S only once a month and always with me around. Last year we planned on the every other weekend thing, but he never followed through and slowly he has just lost contact. This week I told him to keep things to just about S, but he never asks about S so he still is trying to be my friend and hold me as someone else said. I am just ignoring him unless it is important.
What has helped me to detach some over the past month, is the fact that he doesn't care so why should I. However you are getting a D and H wants to be in S's life, which means OW also. I don't have to deal with that. I wish you a lot of luck. I really think what will help is just always thinking of STBX as S's dad and that is it. When you think of him as something else, just refocus on him as S's dad. I also love that you don't want to hate him. I have some resentment, but the thing is that I don't hate H. I hate what he has done, but I don't hate him so we share that as well.
Continue to enjoy your summer off.
Me29 S3 H left 4/1/09 I file 8/2/10 Divorce final 5/17/11 1st http://www.tinyurl.com/25lhu52 2nd http://www.tinyurl.com/2c35ueg 3rd http://www.tinyurl.com/322yk89