Hello, I'm so sorry to hear about your troubles with your brother.

Yes, I am not a doctor, but it does appear something is wrong. I can't say what. Suicidal ideation is common in many illnesses and personality disorders, unfortunately. You say he is in therapy and on meds, so at least there is an awareness of something being wrong. Threatening with suicide is indeed abuse. It is actually catagorized as a high level abuse by the US Army.

Does he see a psychiatrist or only a therapist? He may need a higher level of treatment. Has he been hospitalized? I know that's scary but some people benefit from a short stay while others do not. But if he is becoming a threat to himself or others he may need it. He may at least need a med change or adjustment or something.

It is true that just because there is an illness we still must take responsability for ourselves. I can't just say "well, I have bipolar so I will lay on the floor and let it eat my brain." It is hard, though. Very hard. It is hard to fight the demons, especially if you don't have the right weapons. He can only get better if he wants to.

I say if he's threatening suicide you should call the suicide prevention hotline. Most family members are not equiped to stand up to it. In fact, maybe even call the hotline anyway because you are afraid to go home. They might have advice on what to do.