Everyone who has replied has had some great advice for you. I hope that you continue to hold on and fight. Even if it is not for you, do it for your son. That is what keeps me going, to be honest. They are the only ones keeping me sane right now.
Please get some help, somehow...or there is also another forum by psychcentral,
forums.psychcentral.com
and there is a depression section, and a whole bunch of threads and forums to explore, and people to talk to about this too. (There is even a games section too which helps distract)
Just a thought. But I hope you hang on for your little man.
Feel free to PM me if you want. I understand how you feel.