I can really relate to your post. I am also in a relationship with someone from my past and it is a distance one too (but same state). I agree that 4 months is not very long to know someone and then have them move to where you are. Even if you knew him as a child, you are now dealing with the adult with a drinking past that I suspect he has not revealed completely to you.
Relationships are very stressful, if he is in rehab he is going to come out with a different perspective. Not saying he won't be in the relationship but going to rehab isn't like going to get your appendix out and then you are ok. It is about transitioning to a sober life.
Going to AA twice a day tells me he probably was pretty severe and it is usually much worse than they lead you to believe. It took a good 6 months before I started to see the extent the RABF's drinking issue. It was very severe but initially I thought he was doing great; he was actually very fragile but wanted me to think he was stronger than he really was.
It is hard to be in the situation you are in (and I am as well) but the reality is when they are in rehab, for me it is like putting everything on hold. You already notice he is a different person and if you've not seen the sober person ever, you have to in essence start over.
What is or isn't best for him isn't something you can decide, that will (and should) be up to him. It is a huge change if he does and if he is early in recovery after rehab, big life changes are something that is discouraged because of how it can trigger drinking again.
I guess what I am saying is, it isn't in your control at this point. Recovery takes precedence and it is up to him to tell you what he can manage so that he won't risk his recovery. He is still getting adjusted to his sober self and it is a pretty emotional rollarcoaster ride to be on with them. Be prepared.
Why not step back and let him do his recovery while you focus on your daughter for the time being? You don't have to 'end' things or give up but slowing things down IS a great idea for both your sakes. I have a feeling you are just seeing the tip of the iceburg. I know I was completely naive about how much alcohol takes over their lives and how much work it is to put their lives back on track. If you are going to stay in this, buckle up.
But if you are backing off (which is the best thing I think) then let him do his work and you do yours. He will be better for you and your daughter in the long run if he really focuses on his sobriety.