Hi Kittens Mittens,
Really nice to meet you here in the forum. I wanted to reply as I see some of your experience in my own. I don't assume that my situation is the same as yours but I want to share with you, in case it can help.
I am a man with a diagnosis of BPD. As part of my therapy, I have been getting to know heaps about my attachment needs - 'attachment theory'. I am much more keen as a person, to form friendships with women, rather than men. The reason for this is to fulfill my needs for care, nurturance and emotional support.
We all need attachment figures in our lives, even as adults but its something many of us are in denial about or are just unaware of. My mom has passed and I am not in touch with my dad, so my attachment needs are forfilled by alternative people in my life - my psychologist, an understanding college lecturer who mentors me, the lovely senior ladies who mentors me at my work.
It sounds to me that your friend could maybe be an attachment figure for you. More than a friendship but someone you have a deep reliable platonic connection with. If this is the case, then that level of relationship might feel threatening to his new girlfriend if she doesn't understand how your relationship works. It is very sad but not many people understand attachement needs or platonic relationships. Or maybe your male friend is caught up in this new relationship honeymoon period and has just forgotten that he needs you for attachment too. He may just come round once the honeymoon period expires?
My girlfriend understands and we have talked about where my need for attachment figures comes from. She has come to the understanding that I need to have these people in my life for my mental health to remain well. She initially felt threatened by the idea that I felt strong connection to other women but after discussing it, she came to understand that it is more of a platonic or maternal connection that I have, which poses no threat to our relationship which is a partner/lover relationship.
The challenging thing for you is addressing this because to do so, you are relying on your male friend in explaining it to his new girlfriend. The other thing I always recommend however, that is within your control, is having multipal attachment figures, so that you never feel completely lost if you lose one of your attachement figures. A good psychologist, or psychiatrist, a teacher, mentor, a work husband or a confidant. Just allowing someone in, to mentor you and accepting that as the dynamic of your relationship is enough to generate attachement, I find.
I hope this helps in some way. As I say, our situations may be quite different but I wanted to share in the hope that some of it might help.
Thanks,
Pato