Hello Growing: I see this is your first post here on PC. So... welcome to PsychCentral! I hope you find the time you spend here to be of benefit.

Personally, I don't think you have any responsibility to talk to your brother's girlfriend differently than you talk to anyone else, nor should you. It's not your job to try to figure out how to talk your way around whatever mental health issues your brother's gf may have. Plus... given the situation you describe, I'm not convinced it's even a good idea for you to be talking with your brother's gf about her relationship concerns. From my perspective, I could imagine this might well all come back to haunt you sooner or later in terms of your relationship with your brother. I think if it were me, I would simply tell your brother's gf you're not comfortable discussing her relationship with your brother & leave it at that. From that perspective it becomes a matter of establishing & enforcing personal boundaries.

That said... here is a link to an article from PsychCentral's archives that may be of some interest. In addition to the basic information it provides, there are also links to a number of other articles on the subject. Perhaps they can be of some help:

https://psychcentral.com/disorders/bipolar/

I don't know, of course, if you're here simply seeking advice with regard to this particular concern or if you plan to hang in here with us. However, should you be planning to continue on (we hope you do)... may I suggest you introduce yourself over on PC's New Member Introductions forum? Here's a link:

https://forums.psychcentral.com/new-...introductions/

There's a lot of support that can be available here on PC. The more you post, & reply to other members' posts, the more a part of the community you will become. Plus there are the chat rooms where you'll be able to interact with other PC members in real time (once your first 5 posts have been reviewed & approved.) So please keep posting!