Hi. I've been going through something very similar. I'm still crying. I still want the old life back, but reality is it will never be the same. I've been seeing a counselor and relying very heavily on family and friends.
First - start thinking about yourself and your son. Your son needs you to be strong and happy. Start eating - I don't know your size, but you know what is a healthy weight - get there and stay there. Get outside - walk, ride a bike, sit & read. Even if you don't want or feel like doing those things, as painful and uncomfortable it is, it will give you a sense of independence. THINK POSITIVE - write yourself notes and post them.
"I will get through this." "I am strong." "I'm a survivor." Anything to encourage yourself.
If you are spiritual - pray, read, go to church. Remember that God did not do this, but He will sustain you through it.
Take it one day at a time...now I'm right in the middle of all this too - I've lost weight and have experienced depression...if you can stay busy, focus on you & your son, get out - don't stay at home - be around people - in time - it all sounds easier said than done, but you have to make yourself stop wanting her back and start believing you will be ok.
Hang in there. If she does want to come back - it needs to be on your terms - you have to heal first...
be strong