Hey Audrey - so sorry about this its a tough position.
I find that when I "wish" things like this would happen (I know you don't really want him to relapse) its because I can't make my mind up if I am making the right decision so I prefer the world make it for my by causing something to happen.
I have been with my RAH for 2 years - he was sober 10 years then relapsed last summer. It wasn't a bad relapse. It was devastating to me emotionally and very scary I felt my life was spinning out of control. SR and Al Anon changed my life because I found the tools necessary to change my behavior ( I am a fixer). Now AH is not drinking - its been 6 weeks - and our relationship is much better than before. That's the short paraphrased version - it was a REALLY rough 2 months for me and at times I just wanted OUT.
Today I am glad things worked out the way they did. Tomorrow, next week, or next year who knows - I don't know if he will relapse again. I don't worry about it though, not anymore. I can't do anything about it. Can't control him, can only control myself.
I am also 45 - a little more patient, more established, and childless. If I were your age and looking at my future I am not sure I would pick this route if children were something I wanted. I do know all things considered before I married him I would need him to be at least 2 years sober and active in a recovery program.
You never know what the future holds with anyone. There are plenty of people on this earth that aren't alcoholics or addicts that have problems, issues, character flaws, mental health issues or are just all around assholes. My RAH has some of the classic alcoholic personality traits - he can be very selfish, lazy, a blame shifter, depressed, moody, etc. He also has the biggest heart, loves me like no one else ever has, has been faithful, wants the best for me in life, is my biggest cheerleader and best friend.
Why not give yourself a break on this decision - do you have to make it now? I strongly encourage you to go to Al Anon. Go at least 6 times.
Evaluate the situation later - and if you decide to exit there is nothing wrong with changing your mind AT ALL.