Nope, my ex has no contact with me or his son other than his quarterly payment.
However I have kept in touch with an ex boyfriend, post being a mother, who I was with for 2 years. I still have chats and sometimes see him, but he is very unreliable (as was before) and often lets me down.
He rarely talks about his daughter now even though I ask for news and I get the impression he doesn't see her as much as he did, despite a lengthy and expensive court battle with his ex who stopped all contact when she found out he had a new g/f as she didn't like the idea. I supported him through out, helped him with his case and put up with months of stress and misery which impacted on us all.
Sometimes i think about us getting back together, but in reality that will not happen.
I accept his unreliability now and don't worry about it so much, and much as i miss him sometimes i couldn't ever go back to being in a couple with him. But it's nice to catch up sometimes and we do have a laugh together. I haven't stopped loving him, but i'm not in love with him.
I don't allow my son to see him or know I see him as he was extremely upset after we split saying he wanted a dad or step dad like everyone else at school has and loved having a 'sister' to play with.
Not the same situation as you I know, but as long as you accept the situation and understand you won't get back together it is probably better for your children if you can remain friends.
I would give one word of warning though. If his new relationship is rocky he may well be using you as a pressure release and it might prolong him dealing with that situation as he has someone (you) to talk to and understand and it helps him deal with his home life as a result. I had a 'friend' who told me for 7 years he didn't want to be with his g/f but was always worried about leaving because of the children. After I finally stopped talking to him realising he would never leave her he did finally split up with her less than 6 months later. He didn't have me to help him through it and take his mind of it any more and couldn't cope. Was too late for me by then though. Don't get used as a crutch is all i'm saying.
Gilly