I'm sure many here would agree that post-marriage contact does pull our emotional strings. Remembering some good times from a bad marriage are difficult to keep in perspective, that the relationship failed miserably.
Of course, you clearly are distressed over those times you fall for the manipulation, pressure and "less bad" times. I'll focus on one aspect you're struggling with... inconsistent Boundaries.
Let me explain by describing what many of us have had to do after after the separation and divorce. Even if we have to share parenting, the adult relationship — the marriage — is over. Often we cannot continue as friends, buddies or whatever, the chasm between past perceptions and behaviors versus facts is just too great.
Sadly, it is often self-sabotage to feel you can drift back into some sort of a relationship with the disordered ex-spouse. Family courts don't try to fix the parents. It deals with them
as they are. We too would do well to deal with the ex-spouses
as they are. They're messed up, bad news for us, lacking our best interests at heart and far too risky to buddy up (or let our guard down) with them even briefly.
Which brings me back to Boundaries. Read the articles on boundaries in the
Tools and Skills workshops board. Acting-out disordered people resist boundaries. So it's up to us to establish our own Boundaries to aid us
in response to their actions and behaviors. As an over-simplified example,
we take charge of establishing boundaries... "If you do or don't do ___ then I will do or not do ___."
More specifically, in this instance you need to have a boundary for yourself such as, "I cannot risk getting into a relaxed relationship again with my ex because it always ends up hurting me." Does that make sense?