Congratulations on the little one Surfbee.
With some distance perhaps, yes, separate but amicable is achievable and I think that is a really good goal here. You will have enough on your plate.
While he has "quit" drinking for the time being I wouldn't hold out any hope for that to continue for any length of time, based on history. I'm also sorry to hear he freaked out when he heard, not surprised, but sorry, I'm sure that's the last thing you needed.
I guess you won't know what kind of Father material he is made of until he shows you, but again, based on history I wouldn't get my hopes up too high. He might have moments of being a good Dad though, which is better than none at all.
So how do you get from A to B then. Do you plan on perhaps going no contact with him until the baby is born? That might give you the distance you need to detach from him and the roller-coaster.
One other thing that you can research while you have time is perhaps child support and visitation. Neither one may be an issue, who knows how much a part of this he might want to be, however, it might be a good idea to have something in place (legally written up and ready to be signed) for visitation before the baby is born, if he shows any inclination about that at all.
A visit to a lawyer at some point would be a good idea perhaps.