Hi, Commy,
Sorry you're having to deal with this. Just know that it isn't totally a matter of "choice" when it comes to alcoholism. I'm not justifying or excusing his irresponsible behavior, but when it comes to actual drinking, alcoholics lose the power to choose not to drink. And it generally takes some pretty big losses for them to accept that their messed-up lives are due to the alcohol--that their lives have become unmanageable--and that living sober is the only answer.
Have you consulted with a lawyer? Apparently you aren't married, but a family law attorney can advise you on how to get your financial lives separated. He will be responsible for paying child support no matter what. You will also want a custody/visitation order. Without that, depending on the law where you live, he will most likely have equal rights to custody and if he decided to simply take your son it might be a daunting process to get him back. Do you own or rent your home? In whose name(s) is the lease/deed?
Oh, and if you aren't already going to Al-Anon, I HIGHLY recommend it. It was a complete lifeline for me when I was in the process of leaving my second husband. Some groups have childcare and some would allow you to bring your son as long as he isn't disruptive (you could take him outside if he got restless).