In my experience, this kind of depression usually presents as a woman on her back with her legs in the air.
Sorry to be harsh but I have lived through this and seen it happen to friends and without fail they all left for someone else. In a couple of cases it wasnt because of an affair but because their head had been turned and suddenly that mean that the entire marriage had been shit.
They rewrite history, so be prepared to be told that all the happy years you remember didnt happen, that he was miserable the whole time and you didnt notice or care. Its bullshit, its done to justify treating you like crap.
Dont get sad, get angry. He has treated you and your son appallingly so stop facilitating him. No more wife work, no more contacting him about seeing your son, no providing meals or clothes for your child during his contact time, he does all that himself now.
Remember, he is NO LONGER YOUR FRIEND, you cannot trust or rely on anything he says. Anything he does or says will be to benefit him in one way or another so do not agree to anything without getting advice first, either legal or just posting on here if its something not legal/
Take care lovey, been there, done that and come out the other side, you will get there. 