Mary Alice,
I get a little more of where your coming from. It makes me sad to know you are suffering so much. First, I would like to come and beat your husband up. He sounds like a real jerk. Living like that cannot be good for you. I hope you will decide to get away. It isn't good for you and it is very unhealthy for your son.
I also am concerned about your son. It would be devastating to be without his mom and to know that you chose that for him will have an effect on him that he may never fully recover from. You may feel useless but the worth of a person is not measured in money it's measured in thier hearts and minds. You seem to me to have a good heart and mind.
Is there any way your T can help you to remove yourself from your marriage situation? Maybe if you could break away from that you would be able to focus on your son and yourself and find a way to live a good life. Life isn't without ups and downs but it doesn't have to be so hard.
I hope you will reconcider your deadline to end it all and use that deadline to be out of a bad marriage.
Heidu