The sadness will slowly fade and in time it will be replaced with relief. It's your ego that is hurting. Ego thinks he chose alcohol over his family. The reality is that he chose alcohol over no alcohol. Your ego will prolong your grieving process. Let it go.. Let him go. I envy you... Yup I do. Because even though your son may be crying out for his dad now. He'll be crying even more if his dad stuck around and your child had to watch him fade away, caring less and less about him every day.
In time, when you have healed and are happy you'll have made space in your life for a good man to become your child's father, to become your partner, friend, lover.
You won't feel it right now.. But you and your son are one of the lucky ones. Active alcoholics harm EVERYBODY.
We're here for you in the meantime.