First thing is that I agree with Oldlife. Find someone you trust to confide in. Get some safety net around you - people that know of the life behind closed doors that happens.

Then work out how to get out. He is not hung up on his ex so much as he's a guy that wants his cake and wants to eat it too. I mean he is playing a game, likes to feed the "sweet nothings" to ladies and have them see him as mr. wonderful or something. I am 90% sure he's someone that, if he hasn't already, will cheat on you in the future. He clearly is not the devoted bf that you deserve to have.

You're not stuck and trapped. It only feels like it. Get those trusted friends around you if you're truly afraid, but get out. Run and don't look back this guy is worthless.