There is something here that confuses me... and SJJ, please correct me if I'm wrong; I read through all your original posts but I'm very tired today so might be out of focus.
What I understood is:
- Yes, he cheated and yes, you were part of it. But you also helped him see he might not be wired for monogamy (not an excuse, but I know it's in the personal history of many poly people I've met before they learned to know themselves and got over the shame and guilt).
- He then left his wife and refused to pretend to be mono or act mono; e.g. learning to stand up for himself and not apologising for who he is.
- He tried to be honest with you by texting her in the open and talking about her openly; you freaked out, so he reverted to his learned behaviour of keeping things underground...
- He only lied (from what I gathered) about his flights, when feeling very stressed, cornered and controlled, clearly triggering past (regressive) behaviours for him. Not an excuse but hardly the making of a habitual liar?
- It sounds like every single time you asked him a question he told you the truth, however difficult. For example when you asked if he told her he loved her.
- You have betrayed his trust by going through his messages, and you haven't made sure you took precautions so that you are stable (e.g. have mental health support or meds for anxiety - it sounds like a problems which occurs regularly enough for you to have a management plan and I'm sure you know stress levels increase with major life changes) when you started living together. Of course you were distressed and I empathise, but it still must have been difficult for him.
- He has now made attempts to do poly better; for example taking note of important dates and sharing with her so they can work around the primary relationship; do you give him an positive reinforcement when he does things right and makes efforts, or only telling him how much he's hurt you when he does things wrong?
- Did you make it clear he had to report to you when they use the "L" word or tell you how they communicate all they time? If not, I really fail to see how he was dishonest to you about the nature of their relationship...
I'm sure there are many things I've misunderstood here, but it does sound like you're blaming his behaviour for the difficulties you are having with managing your own emotions and fears of abandonment (and boy, do I understand how difficult this can be), but he sounds like he was under the impression that he'd get to fully express himself when he's with you and then you started putting walls down and changing boundaries which is making him sad and resentful. Just a thought... I'd say you need to try to trust him more
, not less, if you really want to see if you have a future because you are creating self-fulfilling prophecies.