Not really sure if I should be talking about this but I need advice really bad. My girlfriend has bpd. She was sleeping casually with a guy before she met me and then started sleeping with me also, believing it would be casual. When things got more serious between us she didn't stop sleeping with the other guy. I found out a few months into the relationship (I say relationship but we weren't official at the time) and was going to break up with her as I have zero tolerance for cheating. When I discussed things with her at the time she said that it was just because she was out of a long term relationship and was terrified to commit and that because we weren't official it seemed acceptable to her. She begged me not to leave her so I decided to give her a chance and stayed with her. A month later I find out she's been sexting him again. Again I flip out, again she begs me not to leave and that she had no
Intention of doing anything anyways and that she loves me. So I stay again. Months later we are having an extremely bad time and we finally sit down to talk and she tells me all about her bpd. About how she feels impulses to sleep with this guy as (we all work together) his social status at work makes her feels needed and wanted as she can't understand why he would possibly want her. The convo goes on for hours with me agreeing in the end to trying an open relationship so that if she feels like that she can do what she needs to do to make her feel ok.

Now the issues. This makes me feel like shit. Although it's an open relationship and I can sleep with someone if I want, I don't want to. I love this girl. I know (hate) the guy in question who also has no idea about any of this. She also tries outside of this to be friends with him. Is this normal bpd behaviour? Or am I simply being fucked around? I need some advice desperately as I am seriously miserable atm :/  