Hi and welcome!
I would guess that getting a DUI with his daughter in the car has led to quite a few problems for him. For one thing, if I were that child's biological mother, I would request full custody immediately. I bet he's overwhelmed.
Are you wrong to think he could get sober? No, you're not wrong. You are, however, optimistic. Recovery rates for alcoholics are pretty low, even for people who go through rehab and follow-up care.
You talk about "blending your families." If you have children, I would encourage you to read this thread:
http://www.soberrecovery.com/forums/...-yourself.html
And then ask yourself -- is that a situation you want to put your children into?
I had children with an alcoholic. They did not have a good childhood. They all fit different part of the descriptions in that thread. And it is not a situation I would ever knowingly put a child into.
What you do with your own life is your own business. But if you have children, you have an obligation to educate yourself about alcoholism and what the consequences are for children who grow up with an alcoholic. And I would suggest you have an obligation to keep them as far from that situation as possible. But I've been there and seen the fallout, paid the therapy bills, the inpatient bills, called 911 for teens cutting themselves, had kids on suicide watch.