Joy, i am so sorry you are in this situation.
I have been married 14 years and he was kicked out 15 weeks ago. We have a 5 and 8 year old. I have had a hard time figuring out God's will in this one. Fortunately, this AH is not like my first (see below). He knows most of our problems are related to his drinking and he never puts the kids in the middle, thank God. He has neglected them from time to time, but doesn't bad mouth me, etc. I was not and still not getting a clear signal from God although, I have a hard time thinking it is part of God's plan for me to raise these two precious babies without a dad, but right now, we are separated. I don't have to get a divorce within the next 24 hours, so I am not. That 24 hours has been 15 weeks, 24 hours at a time! I have felt very peaceful about this decision MOST of the time during this separation, so that tells me that this is God's will, right now. So, I hope you can find some peace. I know that seems strange to be able to find peace in the midst of chaos, but maybe once you make a decision, the peace will follow. I will pray for peace for you and your children whatever you decide.
And, I want to comment on this... I know it hurts so bad that he would say those horrible things in front of your son. Rest assured, your son will figure it out. I have a 18 and 20 year old from my first AH (yep, i marred TWO OF THEM?!?!?!) and I was so troubled that they were going to believe the things their father said, and that he would stoop so low to not consider his children's feelings, but eventually they knew the truth. I showed them love, caring, concern, kindness, all the things that a parent should do, and he didn't. So, they know. As long as you do the right thing, don't badmouth his dad, it will work out. The was probably the hardest part for me was not wanting the kids to "be in the middle" - but my X was HORRIBLE at putting them in the middle. (they were about 8 and 10 at the time) I just told the kids he was sick. I tried to get them to realize that it is pointless trying to figure out why he does this, why he does that, because he does it because he is an alcoholic. PERIOD.
Again, I will pray for peace for you and your children whatever you decide. Take care of yourself and your kiddos!