Alanon is absolutely NOT about staying...
...and it's not about leaving either. It's not about him, and it's not even specifically about your relationship with him. It's about you, it's about helping you, and it's about helping others in a healthy, non-codependent, non-enabling way. That's it.
If you want to increase your chances that the next man you are attracted to is healthy you will absolutely go to Alanon. If you want to increase the odds you'll just find another *******, then by all means avoid Alanon.
Take what you want and leave the rest.
Cyranoak