She won't reap the benefits of your hard work. If he is dedicated to sobriety, then HE will be reaping the benefits of HIS hard work. Addiction is a disease and it's not easy for someone to recover from. Someone with addiction doesn't "get over it", they have to relearn how to handle human emotions and how to communicate effectively and appropriately, in a healthy way. He never had to do that. Why you think anything will be different between him and his new girlfriend is beyond me. But I do understand the anxiety you feel, because you think, "why couldn't he have got his sh*t together when we were together?" but he hasn't got his sh*t together, and you are much better off out of this relationship. It is not up to you to shape the behavior of someone you want to be with, they should already be healthy, mature, and respectful and loving. You have the opportunity to move forward and to find someone else who IS ready for commitment, and who can give you what you need from a relationship. Take it. There are much better guys out there who you would be much better off with.
"Caring is not an advantage."