he explained that he'd been up til 3am thinking about his situation. He feels like he's stagnated. Life feels like a grind with no way to relax. He struggles to find anything that interests him, he feels volatile and confrontational and without smoking or booze as a coping mechanism, he doesn't know how to reign that in. He feels trapped in our situation and he is riddled with doubt about the future. He has no friends and feels it pressures us to be codependent. He feels like we've fallen into a rut, with no way to get the passion back because we are both stressed out and spread so thin with our work...He won't go to therapy

So...he thought long and hard and analyzed his problem, and his solution is that he should dismiss one of the methods of fixing it? If he feels so stuck and helpless, he needs to muster the humility to ask for help from a trained professional instead of staying in the same rut expecting something to change just because he demands it.

What can I do to improve things? It feels like our issues are so complex, and run so deep, that I don't know where to begin to start putting us back together.

You can't do much for your relationship if you're spread so thin and he is completely unmoving. He needs to see a therapist. It will help for you to do individual and couple's counseling, but it sounds like he's badly in need of some individual counseling especially. It sounds like you're doing work on your own; it's time for him to do it too.