Hi. Welcome to beyond blue.
I am not sure what I could say to make you feel better. But I am listening!
I am saddened by the emotional pain you are going through, when all you are trying to do is help. I suspect this has been going on for some time, but not really sure from your post.
For myself, when I am in a depressive state, I tend to the prefer to be alone. I might send out an email some people in my support circle, but I find that I have the work through it myself. Stupid (?) I know. And because I work with software (logical mind etc.) there is this paradox of negative feelings vs the thoughts in your head that you know are irrational. You mention this about your husband trying to rationalize why he cannot stop crying.
I hope you do not mind if I ask you a few questions.
You spoke in the past tense re medication etc. Is your husband still on medication? Is he still seeing a psychologist?
Have you looked at the resources on the web site here for carers and support people?
I know this next questions sounds a little odd.... but is it you that wants to leave your depressed husband? Or does it want to leave you?
I was told that medication can be a (bit) hit and miss in terms of find the right one to use. And it takes time to come into effect.
You don't have the answer the questions here, but are prompts for things to think about. If you do answer the questions here I (or someone else) can reply. But we are are trained professional. Just people with different MIs, who will help you, support you, in whatever ways we can in this space.