Gracie -
First of all, you are not your mother. Although we all try to please our parents, no matter how old we are, you shouldn't live your life based on what would make your mother happy.
The basis of Alanon is to teach you to take care of yourself and live a happier life regardless of what your husband is doing. I think that the most important thing that anyone can learn is that you cannot control another person's thoughts or actions. Hopefully, learning the Alanon program will help you to decide whether you can live happily with the situation you are in or give you tools you need to leave the relationship. That is up to you to decide.
It is so frightening to think about making that decision but as others have said, you don't have to decide anything right now. You can be married one day at a time. All Alanon can do is teach you ways to live a better life regardless of whether there is an A in your life or not.
The definition of "selling out" can only come from you. Alot of us on this site and in Alanon have chosen to stay with the people we love and others have decided that it is not a life that they can continue with. This should be about pleasing yourself and not others that you are afraid will judge you. I know that it is really hard to do. Since you don't have to decide right this minute, take some time to breathe. Try an Alanon meeting. It can't hurt because you might hear something or meet someone that can make a big difference in your life.
Hugs, Jo