Talking about change and implementing it, two different things. Seems like a pattern has been set and to change that, would need some serious counseling and work.
Maybe time to act proactively and see a lawyer, just to put your ducks in order. Act, not react.
I think anyone that witholds sex from their partner is manipulative.....even if you are disagreeing over something, sex is like Switzerland or time out. I have been in relationship where sex was used to control me, it SUCKS, when they know you have to have it and use it as a weapon.
Your kids will be happy when you're happy, that's the best thing you can do for them.
If you need to hook up, use AFF...no one cares there if your married.
Sorry you're going through bad time and don't have any moral support you can turn to, makes it harder to bare the burden....but, you got through this once before, you know that it's hell for a while but that eventually the dust settles...and life goes on.