Hi MarieLouise,
I am so sorry about what you are going through. I'm glad you have started attending AlAnon meetings, you are headed in the right direction in getting yourself in a better place. The fact that he left and wants a divorce is doing you actually doing you a favor although it doesn't make the pain any easier especially with a child because you will still be connected to him. Alcoholics are best at blaming others for their problems. I still continue to get blamed from my STBAXH.
I was married to my AXH for 11 years and with him for 13 years. After many cycles of him getting drunk doing something stupid (staying out all night, having random men at my house drinking all night etc...) and kicking him out several times he finally left our home about 2 years ago. Since then he has drained our account, had several different women and is still currently drinking. At first I was heartbroken but now realize that it was a blessing in disguise. But it still breaks my heart for my children. We have two boys together. I would suggest to start documenting everything regarding your child so when you are trying to decide what type of custody you want you have some documentation and preventative in place when he visits with your child (if he decides to visit). I'm struggling with that right now trying to keep my boys safe when they are with him. All you can do now is do what you can to take care and protect yourself and your child.