Sorry to hear this. Separation anxiety is very difficult to deal with, especially when it is accompanied by confinement anxiety. With both my separation anxiety boys they responded to having more freedom. Especially with Sunny, I did deal with some destructive behaviour at first but that passed. With Perry it was more along the lines of loss of control and involuntary defecation when he was upset, but that tended to only occur in unusual circumstances. As long as we stuck to a normal routine he coped well, and eventually I had no issues with him at all. But he was exceptional, had the run of the house, and didn't even rip up tissues!
I did find both dogs seemed to want to be able to look out. Access to windows was important, and Perry's one destructive urge was the blinds in the sun porch when I closed them to keep things cooler. He did attack them when I was out, because he wanted to see. I learned to leave them open!
I did find distraction when I was leaving was important. His roller ball with treats kept him busy until I was out of sight. If your boy is losing interest in food this may not work for you. One thing I did do was prepare the roller ball a bit before I was leaving, and locked it in his crate (the only use I was making of a crate at this point) so he couldn't get at it but could see and anticipate the reward. On leaving I would bring it out, put it down on the floor, and ask him to stay until I was about to go out the door. At that point he was very anxious to have his ball, and my "O. K." was eagerly awaited! Good luck.