How will BPD friend likely react?

[Adam B]

I have a best female friend, who is 35yp,  (I am 39yo male) who has BPD, and has times where she has rages, very impulsive, when she has relationships they end in chaos and break-up within 3-6 months, and over the decade I have known her, and gotten close to her, I have supported throughout, been there and cheered up when she felt low and miserable. I have been in a long-term relationship with another female for the past 12 years, but broke up 6 months ago. My friend with BPD has previously said a few years ago  she'd be terrified of having a physical relationship with me, in case it messes up everything that we have together, in terms of a emotional relationship and friendship together, and we have never done anything physical together or slept together etc etc and probably never will.

If I was to start a new relationship with another female, how is my best friend likely to react to this development? 

[mostlyagreeable]

If you haven't said anything about wanting to be with her or loving her, or made it seem like it would be a possibility in the future, then I wouldn't worry about how she's going to react. If she's your friend, she should be able to be alright. However, she might get mad at you and want to leave, in which case you just say "I enjoy your friendship, I hope we can talk later. Maybe you could explain your feelings about this situation over coffee so I could understand?" She probably wants reassurance that it's okay with your new female that you two can be friends. BPD people can be fairly paranoid about the influence of other people on the ones they care about.

Like I said, if you haven't indicated anything about wanting to be with her (at least in three years) then she should be able to carry on.