Hi Iceblueroses,
I just lived through an almost identical scenario with my SO. He has a D20 who is diagnosed bipolar with psychotic depression, whatever that means. But I have BPD pathology in my family and was married to a man with uBPD, and there is no question in my mind that D20 is BPD, perhaps in addition to bipolar. Her older sister (D23) saw a therapist who said biomom sounds BPD, and she is enmeshed with D20 in disturbing ways. They sleep in the same bed, and when biomom had an affair (D20 was 16), she confided about it to her daughter and told her to keep it a secret from SO. Leading up to the divorce, the parental alienation was pretty bad, and D20 handled it by having a psychotic break. Fortunately, it was serious enough that biomom become alarmed enough that D20 got psychiatric services (and a diagnosis).
I could go on.
Like Panda39 mentioned, there is still a reluctance to dx BPD in adolescents, although that is changing. I recommend the book BPD in Adolescence by Blaise Aguirre -- he has a section that describes the differences between BPD and typical adolescence. He also makes a strong case for treating teens as soon as possible while they are still minors and more likely to respond to treatment.
I had a similar experience with SO, trying to raise the possibility that D20 might be BPD, and it was a fascinating lesson in denial. SO and I saw a therapist together for a while, and independently with me, she said, SO is a great guy, insightful, very empathetic, but when it comes to D20, he is nuts I think he had so much conflict with his uBPD ex wife that to see his D20 as BPD was just too much. Plus, he can be allergic to feelings and instead of processing the pain and sadness of having a mentally ill/special needs daughter, he buried his head in the sand.
When I saw he could not take in the reality, I upskilled like a boss. I read Loving Someone with BPD by Shari Manning and Overcoming BPD by Valerie Porr, and started using the skills they describe with D20. SO started to trust that something I was doing was working. And more importantly, I started to use the skills on SO. He is not a rational actor when it comes to D20. He cannot see straight, cannot think straight, and weirdly, I noticed that he has a tendency to treat her a bit like an idiot at times. He also wasn't reading her emotions, basically invalidating her while trying desperately to help her, usually by giving her such basic advice that we started teasing him about mansplaining. I'm pretty sure a 20 year old can figure out she needs a can opener to open a can of beans.
D20 has waif qualities, and her way of hooking her dad is to be helpless, and then get furious when he offers advice. I pointed it out to him, and gave him three or four phrases that might alleviate that dysfunction, and when he started to have better outcomes with her, he began to pay attention to what I was doing.
About self harm, Blaise Aguirre addresses that too, explaining what purpose it serves better than any other BPD material I've read.
Sorry to go on about this. It's close to home for me, and I feel for you. I could see how much pain D20 was in and felt powerless to do anything, and being in the house with them together (she lived with us the last two summers) was a full blown trigger fest.
There is a lot of research that when family members and loved ones have dialectical behavior therapy (DBT) skills, things can improve for BPD sufferers. Unfortunately, when you're the step parent, you may have a bit of a lonely path ahead while you work on the skills without full support from your H. But BPD tends to affect family systems, so your H is probably suffering from the effects in his own way.
I treated SO and D20 as a unit
An example of how you might respond to H if there is a SD13 incident is to validate
his feelings. Or ask a validating question (a fantastic skill), like, "Oh?"
If you start to overreach, he will push you away (read about the Karpman drama triangle). So the most effective thing is to have empathy for his experience, and ask validating questions that put the responsibility back on him to solve his relationship problems with D13.
I'm so sorry you're in this dynamic. It is the hardest triangle I've ever been in.
Welcome to the group
You are not alone!
LnL
