May I suggest that if you are going to complete your studies, now is the most time you will ever have on your hands.
I would also take a part-time job, which is much less stressful, but will make you a lot less dependent and will also allow you to see you relationship rationally.

Motivation is hard to find at the best of times. I'd recommend allowing yourself time to rest and get better when you feel really down. When you feel on top of the world, push yourself to be ultra productive and get the most out of yourself.
That's what I've found has been the only way I could get through - accept the cycles and adapt your life around them. And at all times keep up your meds and therapy, and talk through any possible med changes with your pdoc, especially if you are stuck in a hole.

Hang in there!