With this particular bf - you will have to choose eventually. He says he’s ok with you hanging out publicly, but that will still eat him up and eventually it’ll resurface.

ps - very few BF’s would be ok with their GF hanging out with an ex FWB. I would be gone in a heartbeat.. We all know where the “you never have to worry about this guy” leads, and I think you need to be more honest with yourself and your feelings with him. This decision shouldn’t be so difficult.