Hello. I believe I can be of help to you with this issue.
Well, the general physician doesn't have the training to even know what he or she is doing, based on your reports. Sorry to insult them but really---if the proper diagnosis is missed, prescribing an antidepressant by itself could very easily make his condition WORSE. That is, if your brother has bipolar
I disorder, which is a reasonable speculation or hypothesis at this point (as is your speculation that he might have a borderline personality), antidepressants administered alone often make manic episodes worse.
I wish to heck physicians would stop practicing outside of their area of expertise! He needs to be seen by a psychiatrist for a proper evaluation, diagnosis and medication trial. Another proper initial referral would be to a clinical psychologist who can administer standardized psychological testing and formal structured interview methods to find out what is going on. Sometimes arriving at a proper diagnosis takes several weeks and visits because the full symptoms of any particular disorder aren't always apparent at one point in time. They may show up now, or in a few weeks, or disappear for a short time, only to return. So a longer time line for full evaluation is very often needed.
The traumatic events you describe often trigger a serious mental disorder in persons seem quite normal but who carry a biological predisposition for the disorder. We see this in post partum psychosis
triggering some cases of bipolar disorder, for example. Here is a key point----until he is under the care of a psychiatrist and agrees to go to psychotherapy with a clinical psychologist familiar with the proper types of therapy for severe mental disorder such as this, family members will really just be 'spinning their wheels' trying to be helpful. I believe you have provided a good summary of just how ineffective all family members and the approaches to 'helping' have been to this point.
Do not send him back to your general physician until you really know which disorder he actually has. A psychiatrist for example, might conclude he has bipolar disorder and he will be tried on a mood stabilizer, not an antidepressant. Logic and trying to placate or reason with him will simply result in frustrating interactions with him. It may take a serious emotional breakdown, a legal crisis (breaking the law and getting arrested, a DUI, etc.) to force him into proper treatment. Family members DO need to get together and plan a common strategy they can all stand behind, without wavering e.g., he can receive no help or support from family except based on his compliance with visits for a full evaluation, etc. Everyone needs to get on 'the same page' about how to support. But no one can really do much or 'fix' this because he really needs a treatment PROGRAM.
I'll pause here and solicit your reaction to this post.