Hi. I feel your pain. I've been there and done that.

I think it's our extreme insecurity that can cause us to think that our SO is cheating on us. It's hard to accept the SO's opposite-sex friends, and hard not to wonder what's really going on when we're not around them.

The strange truth, though, is that, the more we think our SO is cheating and/or accuse them of that, the more likely they are to end up actually doing it.

I'm sure you have a lot to offer your fiance, but are having a hard time seeing it because of the awful negativity that BPD brings with it. He obviously thinks you're special and has chosen you to wear the ring he bought.

I think the best defense against such problems is to construct a solid life for yourself that is independent of the SO. A routine that might involve hanging out with your friends, indulging in your hobbies, exercising, whatever. Me time ! Spend some time with yourself by yourself, realizing what you DO have to offer your fiance and this world Even in relationships, it's essential to maintain your own identity and your awareness of it. You are entitled to your life and your guy friends, as much as he is to his life and his female friends !

When we become co-dependent with the SOs, we run the risk of losing ourselves. If they then happen to leave, our world comes crashing down.

Hope this helps in some small way. Please be kind to yourself