Originally Posted by SchrodingersCat
On one hand, you tell him it's okay to be nonmonogamous with you. But as soon as you "have" him, you change the rules. You tell him you now want monogamy. You didn't mean it as permanent, but that's not how it would have come across. You changed the rules to make your relationship more like the marriage in which he was trapped. So he changed his behaviour to be more like the husband he was in that marriage.
He doesn't trust you to be truly comfortable with nonmonogamy. You need to earn that trust with permission that you don't retract when life gets tricky. For where he is right now, if he's going to learn that polyamory can work, he needs to do it on his terms. From your perspective, boundaries are reasonable. I agree. However, for him, right now, those boundaries are more likely to make him return to his old ways.
Exactly. And I agree - he has to learn to be accountable for his behaviour. But when he did try to be transparent and show her facebook messages, she reacted badly. And the OP also needs to be accountable for her behaviour, and how it triggers him.