Please, get to the peer counselor. There is nothing that they haven't heard, and every one of us have thoughts that we shudder to have hit the light of day.
If you didn't have Marc and your mom, you could run away. But you do - and thank God for them everyday. Then, do what He needs you to do. Take care of you so you can make sure that you can do what needs to be done for your son.
You don't have strength to do it. I've read that not many of us do. But you can with God's help. He sent those pastors to get involved in your life. Now, you have to meet Him half-way.
I think that Michelle might be right about Gabe. Take your emotions out of the equation and get the authorities involved. Does his family know that he is a dead-beat? Can you contact his parents and tell them that Marc needs things to be provided by his father?
Read the tag line under my signature, hon. Get in touch with me in the alt univ for a number if you want to talk...