Depression and mental illness is something I know well. From own experience with it and that of my partners.

He seems like he is in a state where he doesn't totally like the situation he is in but also doesn't have the energy, feelings or know how to get there. Problem is, even if he did get what he is searching for its not going to fix his insecurities which seems like are the base of what is going on.

He may need to get into some sort of therapy and maybe working a few things that at least I can identify:

Working on his self worth. It took me years and I still have problems with it but learning that I am worth something to the people around me helped me huge in my relationships and even friendships. I still cannot pinpoint why people want me around but I find strength that it must be something and I am enjoying learning what those things are.

Finding out where these insecurities are coming from. How long have been around, what emotion do they stimulate (aside from envy) and how to combat them.

And something I am learning lately. That I am responsible for the relationships, my happiness and how I function. Not saying one is able to will themselves to be happy but that being with someone isnt inherently going to make me happy. That its not my partner's jobs to make me happy, it's mine. Dont get me wrong they help, they do amazing jobs at it. But if I am unhappy I have to find the courage to work on and fix it. If I cannot then I have to find other means to do so.

I am not a professional in the industry but I have been dealing with my mental illnesses, recoveries and the slew of meds that I have been on to find what has helped and my whole polycule have a long to go but I hope any of what I have written makes sense and doesnt sound trite. You cannot make him to anything, you cannot make him better and its good that you see that however maybe suggest these things to him like getting into actual therapy as well as looking at what other meds are out there.

Wow this turned into and essay, sorry.