Joel
As someone who married 'that one' years ago, it ended in very tragic. You are asking logical questions about an illogical person/events. How 2+2 equals 7 will never make sense.
I can't express how lucky you are at the moment. You have a choice without kids, house, hospital bills etc.. You do have a broken heart. It will mend over time. Just know you aren't alone and have compassion for others you meet down the road.
Please take other path. You can still pray for her, just close that door.
Edit:
COD is right on. I was down that same path with two kids, house, passed out wife. She died in the end. Your choice.
AG