Your comment about moving your remains to the U.S. means that you have at least one positive thing to live for and/or that you care about something or someone a lot. Though more than likely, you have many, many positive things to live for. So even though you say "none of this matters anymore," everything does matter! It's that when depression hits, it's hard to see all the positives in life because depression warps our thought processes; it makes us feel like failures etc.. But we shouldn't let it. It's hard as hell to fight it -- I would agree -- but we've got to do our best. If that means going to the hospital, then we should do it. Your family matters, your friends matter, your fiance matters, and most of all, YOU matter.

I know you can fight this. You have to do what you need to do. If that means going back to the States, you should be proud of yourself for getting into a PhD program and giving it your all. Not many people with BP can say they've gotten into a PhD program.