This is a repost from a similar thread, but it's relevant to you too.
I had an LTR with a BPD woman for 4 years when I was in my 20s and I can tell you from experience, it's nothing to laugh at or take lightly. It's particularly damaging for AFCs locked into a BPDs negative feedback loop, especially when he's developed a soul destroying ONEitis with her and associates himself as the source of her depression / psychosis.
True BPDs progressively convince their victims that they are the source of her neurosis. You are not yourself, you are who she's molding you to be, and eventually you'll come to believe that it's in your best interest - indeed, your responsibility - to be who she wants you to. You will gradually give up on your family and friends (or they give up on you), you will drop all ambitions and passions that directly focus on you, and you will abandon any genuine, independent identity you held for yourself, all because these are threats to the neurotic narrative she constructs for herself and lives out.
She will reward your conversion to her psychosis with intermittent, crazy sex, but this is simply the reinforcer to keep you locked into her narrative. The YOU you know will cease to exist and the character she creates for you will take over. This is especially true for beta chumps who see their BPD as their best, only option for a long term romantic prospect. She's an HB 9 (to him) and he's never ƒucked better than a 5 in his whole life, so the risk of catastrophic loss is real and ever-present.
In the latter stages of a BPD relationship you will get to the point where her overt cuckolding of you is an acceptable situation. You think you'll mitigate it by negotiating some "open relationship" status with her. You will internalize the reasoning that negotiating for her desire is preferable to losing her. You'll propose that an open relationship means you're both free to ƒuck other parties, when in reality it's the only way you can rationalize for yourself the fact that she's going to go ƒuck other guys, and you're going to accept it because you're locked into her neurosis. That, or the mere suggestion of you being interested in sex with another woman will send her into fits of jealous, histrionic rage.
You're living in fear. You're afraid she'll commit suicide if you uproot yourself (a classic BPD unspoken threat), but trust me on this, it'll be you who swallows a bullet before she ever will. I've known 2 men who've done just this, and another who hung himself as the result of a BPD relationship. I know it seems like most of the guy's here are simply passing you off by saying "get out" and move on, but your life literally depends on you doing so.
Also, I must add this, when and if you do finally muster the self-concern enough to actually leave her, expect a complete 180 in her mentality and behavior. One thing a true BPD loathes more than her victim is the thought of having to ensnare another. There are plenty of other AFCs ready to fill that role, but the comfort and easy predictability you represent to her in the present builds an emotional dependency. BPDs will fight like wild animals not to lose their victim; like I said, expect an extinction burst from her. For a guy so accustomed to her neurotic behavior, his first impression is that she's making some real change for him in order to "improve the relationship." It's not, but so radical a shift in her behavior will convince you otherwise, and cause you to doubt her deception, particularly when you yourself have no options and believe you'll never do any better than her.
