That to me is the hardest issue with trust violations. After the first few i always experienced each one anew every time it happened. Im still working on lettng go of the past shit even though were not in that place anymore. I dont think i could have done it while my trust was still being abused.
Counselijg might not be a bad idea for gettng help with trust issues. Obviously you need to make sure the counselor is poly friendly. Im a bookish type so i tend to go for books on trust. I got a really good one that talks about the connection between our childhoods and how we deal with trust. If certain needs didnt get met as a child were more fragile around it as an adult. When i get home ill find you the name.
If he truly cant keep your boundaries than you have to decide what you are willing and able to live with. Hubs and i separated once years ago because i told him i just couldnt stand the lying. He thought it was an ultimatum but it wasnt. It was my boundary of what i wouldnt tolerate. We still saw each otheer but on a more casual basis and that space and casualness was good for me because i didnt have the same expectations of him. He ended up figuring out he was being stupid (his words not mine) and we got back together. Sometimes space is whats needed in order to see the big picture and be able to make a better decision.