Girlfriend in group home

[Loverboy21]

I met my girlfriend 3-4 months ago on an online dating site. We hit it off instantly and just about every minute we spend together is pure bliss. She is an extremely intelligent person, so it's hard to tell when she's manipulating vs just justifying her disrespectful actions through her condition. She has always told me how much she loves me and is afraid to lose me.
Circumstances have made it so that she is staying In a group home for the next few months, and before she was sent away I emphatically promised over and over that I would be there for her when she got out. I recently found out through her mother that she openly gave her number to a guy she saw in public a month or two ago. (This was before we had real talks about her insecurities and more reassurance on my part that I wouldn't leave her for no reason). I found this out from her mom last night, and she's been in the group home for a week or two now. I've done a lot of research today about the abandonment issues common in people with BPD. And although I don't think she's cheated on me during the time we've been together, before she was sent away, her mom also remarked on her wearing a necklace she "got from me" (really from another guy). She also admitted to her mother said that she would be afraid to work at a potential hostess job because of the temptations around her. She is bisexual and in a group home with all girls, so that's making me think that, while she still does love me, she will follow her destructive impulses and get into some sort of trouble at the group home. The only way we can communicate is through letters. I want to let her know that I'm here for her to support her, but only if she seeks treatment. Also that the only reason she would have to believe I'd leave her is if she cheated on me/ continued the emotional disingenuousness. I thought about breaking up with her through a letter but I think it's important for her to know I still love her, but that I need her to use this time to seek help so that we can continue our relationship in a healthy and transparent way once she is out. Any advice?

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[Domino]

Hey Loverboy (great name)

It sounds like you need to address your concerns openly and honestly. It may be that the necklace and number are perfectly innocent and you are getting yourself worked up over nothing. Or perhaps, given that you are still early days, your girlfriend felt it was ok to get another number and didn't realise this was something you would be uncomfortable with.

My advice would be to make it known how you feel. You have to be able to trust your significant other. Try not to be accusatory or blaming. Give her an opportunity to explain - it may be perfectly innocent. Set out your boundaries. It may simply be that you have different ideas for what's acceptable in a relationship.

When I first got together with my other half, we dated a few months. She spent ages asking me to 'make it official' so that we were exclusively boyfriend and girlfriend and I was always a little hesitant (we're long distance and I wasn't keen on that). Anyway the night after we were 'official' she told me she kissed someone at a party. I was mortified. It turns out she just had no idea this would upset me. Her previous boyfriend had apparently been fine with this sort of thing. Anyway, after I explained why I wasn't happy, she apologised and I've never had any doubts about her commitment and faithfullness.