For probably a good four or five years of my relationship with my fiance, I was extremely depressed. I think my fiance had an easier time of dealing with it, though, because we were long distance for most of the time. When we finally moved in together (and several states away from both of our families), I was forced to grow up a little, which I think helped my depression some. I still struggle with both my depression and my anxiety, but it came to a point where I had to actually want to get better, not want to allow myself to wallow in my depression, which is a lot harder than it seems. Getting better is terrifying because for so long, you've only know the hurt and pain, which is so much more comfortable than pushing yourself to be better.

I think couples therapy could be helpful for you; it might make your fiance realize how much he's hurting you, and that might be the push he needs to realize he needs to want to get better to save both himself and your relationship. I would probably hold off on planning your wedding until he starts showing real attempts to get better. Possibly check out the book Stop Walking on Eggshells. It's written for people who's partners have BPD, but it also talks about remembering to stick up for yourself and care for yourself.

One side note, I was on a variety of different medications for 5 years and went through several different therapists over the course of 7 years (I'm in therapy right now), so it definitely takes a lot of work to find the right medications (if you need them; I don't take them anymore), and the right therapist.