just want to know what I can do to show him I'm serious about not putting up with this anymore.
I think you already have. You said "He had a bad night in October and I told him to get it together by December or I'm done". Are you done? The problem here is you can't make him do anything, so you have to be the one to "do" things. You could ry setting a boundary that you won't have him drink in the house. You could try and set a boundary that if he does this or that one more time then you will do this or that one more time.
At the end of the day when you live with an active alcoholic, really, the only thing you can do if you don't like it, is leave it. Since you have already said if he didn't get it together by December that you would be "done" you need to be done. Otherwise you are making false statements, and become like the boy who cries "wolf". If you aren't prepared to leave then I suggest you start going to Al Anon to get the support you need to deal with this in making decisions about your present, and future.
A word of advice NEVER, ever, utter a boundary unless you really mean it. If you do this time I suggest going to see an attorney and get your ducks in a row to prepare.