The realization you are making is an important one. I too came to that conclusion: even IF my exAH sobered up and found recovery, he was still a crappy human being and a terrible (abusive) husband. I too put out this image of strength, but I was crumbling inside.
You're not "supposed" to do anything except what is right FOR YOU. I know it's a weird shift to start thinking about your life in terms of what's good for YOU, instead of what's good for HIM, but once you get used to it, you look back and wonder how you could have thought otherwise.
As for the guilt you're pilling on yourself, let it go. The path you have taken was *necessary* in order for you to come to this point in your life. I call my path "a necessary evil", because it allowed me to finally realize I needed to stop letting others treat me without respect and love. Had I not married the man I did and had a child with him, I would never have made that realization, taken action and changed my life. I would not be who I am today. With that reasoning in mind, I am thankful for that necessary evil.
You can do this. Your sister may be moving, but you can and will develop another support system. In the meantime, SR will be here.