Sometimes you have to detach from a child who is under 18. We moved heaven and earth for our difficult child 1 and she kept doing what she was doing. We did try an Residential Treatment Center (RTC) and it kept her safe for 8 months to the tune of $50,000 dollars--I am hoping part of the reason she can take care of herself now is from that experience--otherwise it was a waste of money since she relapsed and was worse than ever after coming home. She went to a dual diagnosis rehab when she was 17 for drug abuse and basically living on the streets.
For our own mental health and the health of the rest of our family we had to emotionally detach from her before she turned 18. It didn't mean we didn't do everything we could to help her, it meant that we got on with our own lives and didn't jump on the roller coaster with her. It meant we didn't consider ourselves failures because of the choices she was making. It meant that we were upfront and unashamed when talking about her to other people--we did not let it reflect on our own sense of worth. It meant we went dancing and had fun with each other. It meant we could count on eachother for support when one of us was feeling upset about her. My husband (her stepfather) and I became closer during that time and my love for him has deepened because of his love for this stepkid who has been so difficult. He loves her despite all the trouble, financial difficulties, etc.
Once she was 18 we had to detach physically as well as emotionally but we now have a success story--a difficult child who is making it on her own under her own terms who loves her family and is able to connect with us again.
I think your husband loves you and your kids very much and is actually reacting in a very healthy way. I hope you will get some help with the depression, please don't let your marriage fail because of a difficult child.
Hugs,
Jane