You are absolutely right. His communication with ex's is NOT ok. But he doesn't understand. Even as recently as this summer I became friends with my ex-OM and his new gf again. There was nothing inappropriate, even feelings. But I didn't understand that the behavior, the contact would hurt my H. I'm not proud of it. It isn't something a bipolar can think about really. It's sort of like living in a crowded room full of fog within your own mind. Some things seem perfectly logical to you and things that should be evaluated in connection never occur to you (like how your actions appear to and affect your spouse). It sounds like an excuse, I know. But it really is a product of a mind in turmoil. And during those periods of clarity it tears him apart that he is hurting you.
I suggest you not file for D, and if he does do everything in your power to prevent it. If he really is bipolar then once he gets well he will be devastated by what he has done. He can get better, of that I am certain. And when that happens he will really need you. The guilt is very painful (not that he/I doesn't deserve it), and he will definitely believe he deserves it if you choose to leave him then. When I tried to get a D I didn't really want to be without my H, I was trying to stop hurting him.
I also suggest that you keep looking for a therapist of your own. Ask in advance if they are a specialist in bipolar disorder and SBT. These are good principles (DBing) and you need a counselor who is supportive of the choices you have made concerning how to approach your life and relationship. Once you find one they can help you cope with the really bad days and the healing once he is ready.
Hang in there...I'm here for you.
undefeated 24 H 24 S's 4, 2, 1 M 5 yrs
"Most of the important things in the world have been accomplished by people who have kept on trying when there seemed to be no hope at all." ~Dale Carnegie