You are absolutely right when you say this isn't about him, it's about you. Why do you fear losing him so much? That's not a question that needs to be answered here in the forum, but one you have to answer for yourself. He is an alcoholic. He might be sincere about recovery, he might not. He might be having an inappropriate relationship with another woman. These are the facts. There is no amount of worrying or changing you can do that will change the facts. The only thing you can do is live in reality, and that reality seems to be that this may not work out the way you want it to. Can you be okay with that? If not, why not.
I am in a relationship with a man that is not an alcoholic. He doesn't have any friends who worry me. Yet, even though we have been together for five years, I still realize that it may not last forever. He could change, I could change, we both could change and that could mean the relationship ends. I would be sad if that happened, but I don't live in fear of it. I know my life would go on and I would be okay. Do you know that about yourself? If not, why not? There are no guarantees. We get what life gives us and sometimes it's not what we want. Our job is to be able to survive and thrive regardless of whether things work out great, or not so great.
I agree with LifeRecovery. A therapist helped me to sort out a lot of stuff I didn't even realize needed sorting. And my life has been so much better because of it.
L