I've been wrestling with my BPD wife's issues for a few years now. With a LOT of patience and research we've tackled a lot and have entered therapy to work through our issues. One thing that seems to work for her and get her stabilized is sex. Not just sweet cuddly intimacy but hard dominant pounding seems to give her a sense of security in our relationship that she referenced quite frequently. My only concern is that as we age, this may not be an option anymore but I do know for now it seems to balance her out biochemically. I think a big part of it is that she doesn't trust her emotions and the BDSM lifestyle gives her something of a framework to function within. She's also specifically into DDLG play which I attribute to her nonexistent relationship with her biological father growing up.  I'm her second marriage. She was with her previous husband from high school and he's extremely passive aggressive and timid about confronting her directly about emotional things. When my wife splits she has a field day with him and their exchanges quickly devolve into nonsensical shouting matches or email flame wars. Having dealt with depression myself and multiple relationships with individuals significantly older and younger than me I have a few more methods for dealing with her flare ups. The DDLG dynamic allows me to take an authoritative tone and walk her through sticky emotional situations where she exaggerates or minimizes her behavior. Growing up with a lawyer as a father has enabled me to deal in this situation that is rife with perpetual debates. Idk. Spankings, nap times, cuddle time, daddy daughter dates...they all seem to work. I know it's not for everyone but it seems to be working for us.