I respect you for your self-examination. it's not easy to confront our own beliefs.
I went through something similar, although not identical, with my lover (who I formerly called FWB). although our relationship was all but over, as soon as I started seeing someone else he started having issues with possessiveness and jealousy. it was really messy for a while, but he spent a great deal of time in self-reflection and we're now finally able to negotiate comfortable parameters for our relationship.
during the roughest part of our crisis, he could not touch me sexually for a while. he couldn't bear the thought that I'd been with anyone else. it took him a while to sort out why he felt the way he did.
solo polyamorous pansexual queer biological female with Aspergers.