Is he seeing anyone else or is he living alone? Just curious. I find his behavior strange. If he wants separation, why isn't he pulling away further?
Is he trying to take advantage of both worlds, his other (single) life and at the same time keeping his family life when he wants? It's selfish. Maybe he needs to understand that this is causing you pain and not working for you.
This could be a long ride. Detaching and setting boundaries is mostly to protect you. The question is how long can you handle this without losing your mind?
Also, if I remember correctly your H likes to control everything (like I used to). If you detach and set some boundaries, he will feel that he doesn't control you anymore. This should make him feel that he is losing you and that he doesn't control the situation anymore.
Me:49 XW:41, M:18 years, Kids: S18,S14 BD:JULY 2017, W moved out: DEC 2017 Filed for D: APR 2019, D Final: JULY 2019