Serious Marriage issues...family influence?

Hello...2 years ago I married a women whom I had known and worked with for close to 3 years. We dated for almost a year before deciding to take the plunge. About 6 months into our marriage my wife became ill and was placed on medication including steriods to help with pain. Over the past year and a half our marriage as reached the brink and my wife has dropped into a deep depression. She has directed alot of her rage towards me when I have done nothing but support her throughout the entire 2 years. My wife has children from a previous marriage and I have been the mother and the father to them during this period while working full time and maintaining the home as well. Friday she reached the end of her rope and I ahd to make a decision to seek help for her since she would not for herself. She is now getting the help that she needs. My family is encouraging me to leave her and file for divorce and begin a new life, but I can seem to get the courage to give up on a women with so many issues, regardless of how mean and cruel she is to me. At times I really want to leave, but cannot do it. I dont understand why, it would be great if someome could help me understand why...Thanks for your help and time...