It's a really useful post thanks Mutt it has much resonance for me.
I too have been caught with my mum and sister in triangulating with my h whilst looking for support and validation. What I got was an ' oh well you made your bed now lie in it ' response. ( thanks mum

) I am guilty of saying too much about my h in a fashion that is not productive for either me or my marriage. Like you I was looking for support, but at a deeper level I am aware that my family were never happy about my relationship with my h (so why go there for support ) and when they were unsupportive I was able to displace a lot of my anger at the issues within my marriage and direct it at my mum. ( this was promptly deposited with my T

)
For me I now realise that dealing with all things BPD is better when the person I am asking for support from has an understanding of the complexities of this illness.