Hi daring, Sorry to hear about your son and his sitch. Just remember, he is hurting because of H's MLC as well as you. My D19 has been staying at her boyfriends apartment since coming back from her trip last week. I talked to her and told her that I didn't think she should be living with him and that's pretty much what she has been doing. What she said really hit me..hard! She said "But it's so NORMAL here, not like at home and with mom acting so nuts!".
I realized that the kids are taking this harder than I thought. Even at 19, she just can't understand why her mom is doing what she is. She talks to me about it a lot and about how "crazy" her mom is acting and how she doesn't want to stay at her place but feels like she would be hurting her mother if she doesn't (she hasn't yet stayed there but has been there 2 times). She says that when she tells my W she was staying with me her mom gets upset and looks "sad".
If your son is just out of major depression, H really shouldn't be talking to him the way you described. He needs guidance yes, but having had to deal with major depression in my W, it's easy to say the wrong things. He's trying to deal with the changes at home and in his father just like you are. I realized that while my W was still living at home, I was spending so much energy on my M and my W while mom was just acting out and denying, it had to affect the kids just as much as me and my W. Of course you have to make sure S16 isn't being disrespectful and breaking the rules or just plain ignoring you but at the same time I'm sure he is angry and confused and add on the depression and he must be hurting. It's so normal for 16 year olds to 'split" the parents. My D did it like a champ. But after she got a little older she stopped (part of me thinks she blames herself somewhat for W's leaving as how to deal with her was the biggest thing that we used to fight about).
I guess all I'm saying is just remember that with your M still "up in the air" I'm sure S16 is also feeling the home and family as "unstable" right now and that's a lot to deal with, even at 16.