Hi, people leave marriages all the time when there's illnesses. That does not make you the bad person. You are not married to the illness you are married to the person.
If the person does not make you happy then your son is seeing that. He will think this is what a marriage is like.
If you leave he will see you happy. He will see you in a happy relationship.
My father left my mother due to her mental health issues. Mom was not alcoholic. He actually was the drinker. He slept on the couch for seven years and divorced when the youngest turned 18. I wish he would have left when he was unhappy. It wouldn't have made me so codependent.
There was adjustments that I had to get use. I was mad at him for making me have to take care of mother. (Which now was always my choice) We have worked those issues out. As long as you continue to have a wonderful relationship with your son he'll understand.