As powertools says, you are not a monster. You don't sound like a terrible human being to me either. Monsters don't care who they hurt; you care deeply.

Many years ago I made a fool of myself, ruined two relationships, and hurt men I supposedly loved because I couldn't see past my own fears and dependence, so no, you are not the only one to feel this pain and remorse. But at the time, I refused to acknowledge that I was ill and I repressed all emotions having to do with my failures, until decades later they flew up and hit me in the face like a stepped-on rake. Far from being cowardly, you are confronting BPD now and experiencing the pain of your loss in its due time, working through what you and your friend did and didn't do in the relationship, and that takes courage. Please don't use your intellect as an instrument of self-torture. It appears to me that you have what it takes to make it through this.