This is a tough question. I have to go with my own experiences to answer this one. I fell in love with, and married, an undiagnosed bipolar. It was hell for the first several years (pre-diagnosis and treatment), as I did not know how to help him. Bottom line was, I loved him, so I stuck by him because I wanted to help him face the demons. It sure was an emotional rollercoaster back then, but 23 years later, we are still married.
I made a choice to stay with him and not abandon him. He had no idea why he acted the way he did. I could see how tormented he was by his actions and how it affected us. Serendipity smiled on us the day I got a position working for a crisis stabilization unit. The very first day, I encountered someone suffering from manic depression,and the "ah-ha" moment hit--hubby wasn't suffering from just depression--he was bi-polar.
You can't choose who you fall in love with; you can only choose whether or not you will stay in love.