You are as much caught up in his alcoholism as he is judging by your comment below:-
"I'm not going to leave him, I never intended to, I didn't start this thread to ask "shall I leave my partner". He's my other half, the father of my son, I will help him him and love him every step of the way however difficult it gets. If I leave him, what reason does he have to stop drinking? He'll drink himself to death. He wants to stop, he knows how bad it is. If I was one of the Brave Bus ladies I'm sure you wouldn't have advised that my partner should take the baby and leave me? "
Alcoholism is a family disease.
What makes you so sure that you can beat his alcoholism?. You cannot and that is the long and short of it. "Helping him" and "loving him" like you are is not helping and what you have tried to date has not worked because you cannot help someone like this. You are his codependent enabler. He is telling you what you want to hear, look at his actions and what he does rather than just hearing his fancy words.
As for your comment re the brave bus ladies why should your partner take the baby and leave you. No-one has suggested that so where have you got that erroneous idea from?. It should be you and your baby leaving him actually.
He is already drinking himself to death and you can do nothing to stop that process in its tracks.
If you stay as well, what incentive is there for him to stop drinking?. You will carry on enabling him and propping him up and by then as well it will not be just you seeing all this but your child as well.
You wrote earlier that, "I don't want to inflict an alcoholic dad on my son, what I want is for him to stop drinking and be the kind lovely dad I know he would be..."
These two aims are incompatible with each other. By staying too, you will inflict an alcoholic dad on your child.