<human>: I've been with my SO for two and a half years now, living together for one and a half. She has had very rough life which resulted in her developing C-PTSD and major depression. Her C-PTSD makes her behave like someone with BPD, which was her main diagnosis until very recently. 

Basically, she used to be way crazier than she is now, but after starting a DBT program a year ago she has improved ten fold. All that really remains is the depression, minor mood swings (no more significant splitting), and a total inability to handle minor/major stress in day to day life. This means that she is loving and happy when nothing major is going on, but as soon as she has to work/go to school she becomes very depressed for a variable period of time. 

It is almost like I have two girlfriends, the amazing one I see on breaks/weekends/vacations, and the negative, irritable and depressed one I live with all week. I used to struggle with depression, so when she get's depressed for an extended period of time it is very hard for me to not get dragged down into being depressed myself. It is very very difficult to bring her out of a depressive mood, so my only options are to try to ignore it/not care, distance myself from her, or get sucked into it with her. Obviously, none of these are very good options. Is there anything I can do here that I'm missing? I'm very bad at these things. Honestly, the only things I've found that keep me from not getting depressed as she unleashes a barrage of negativity on me about small every day things is to 1. try to think of something else 2. mentally build a wall around myself 3. be under the influence of drugs/alcohol 4. leave and do something else. Is there any skills I could be doing to make myself less susceptible to it? or is this just a "get used to it or leave" kind of thing? any and all advice welcome.

we are already in couples therapy, and I have a personal therapist too.

Can you give me the gist of the text in a nutshell?
<bot>: girlfriend gets depressed/crazy literally all the time about small things. This often makes me depressed, and the only way I know how for this to not depress me is to distance myself from her.