I know it is past due to be saying this but I felt a connection and I felt like I could relate to you. I have an eight month old daughter and so often I have imagined the same thing in my head. But I would not and could not leave her.
My mother's mother committed suicide when my mother was only 3 years old. Though my mom was too young to remember the tragedy of what happened, she was too young to remember her mother hardly at all.
You are such a significant woman in your child's life and no person or thing could replace that. You have an opportunity to show this child the way life should be and let him feel all the happiness in the world.
That thought alone helped me to be strong when I was having those weak thoughts. I would just go in my baby's room and hold her so tight and cry, she is so innocent and so dependent on me to be there for her. I knew that I was weak and was hurting and it may sound bad but she helped me through it by just being there.
I want to be happy for her and certainly for myself. I think it is very important to heal yourself first. Possibly if you have a trusted family member or friend that could take him for a few days, this way you could sleep and relax and take some time for yourself. "You time" is definitely one of the best antidodes for saddness or depression.
Take my word for it, I did it yesterday and the day before.
Good luck to you. Be strong until you can find that peace of mind and happiness.