Hiya SeattleJo,
I just joined these forums this week and just took my first step (finding an apartment) in leaving my alcoholic husband. The house we live in is his from before we met, but he's never actually been able to afford it on his own (found out after I moved in that his parents were helping him every month). I'm in a similar position as you in being the primary earner in the marriage. I pay the majority of the mortgage and have invested well over $50k in the house in our 5 years together. In truth, my willingness to (over time) take on so many of the bills is probably what allowed him to be able to afford to start drinking at full capacity.
I'm feeling tremendous guilt over leaving because he seems so vulnerable and weak in life. I have to keep reminding myself that he's in all of these vulnerable positions because of his actions and decisions. I had nothing to do with any of it and yet still feel tremendous responsibility in wanting to make sure he'll be okay, even more than I'm thinking about myself most of the time.
I know I'm going to be supporting both households for a period of time and it stresses me out a lot. But being in this house with him is also so tense I have chest pains every day. I'm picking the lesser of 2 evils, I think.
It's seriously hard though. I am going through mental and emotional gymnastics every day.