After this long of a thread, I couldn't possibly frame anything too wise. I peeked back a little bit and do have something to say, but perhaps you should start a new thread that summarizes everything to this point.
If I read it right...you are still friendly, but he's separated and looking for someone else to hook up with. So, basically you are his safety net. My advice is to remove the safety net. Do NOT be all nicey-nice with him. Don't be around to get your butt slapped. Don't even dream of being physical with him. Ideally, you'll reduce the relationship to entirely business-like. If he's shown interest in you, then I'd wager he will respond to having you withdraw from him. He'd especially respond to the thought that you may be looking for someone new.
Don't argue, "it'll push him farther away". It won't. You be a challenge and he'll want what he can't have. Be what he can't have. And get busy with your life. Be unavailable. He must have the kids sometimes...be gone when he has them.
You cannot be lonely if you like the person you're alone with. Dr. Wayne Dyer
