Mel welcome to SR im so sorry to hear of your troubles. Firstly you need to get help for yourself, Alanon and help is here in SR. It will make you stronger and you need to be strong for your son. You ask "when do you know when enough is enough"? I think you already know the answer to that question.
I posted here read lots of books "under the influence" and "codependant no more" it gave me the knowledge that i needed to survive, and helped me make the right choices for me and my kids. alcoholics will stop when they want to, not when you ask them to, sadly some never do stop drinking. You have to ask yourself how many more years do i waste, is it fair on me and my son.
My heart bleeds for you Mel. I am very glad you found SR this could be the start of your recovery. Take care.
Mair x