Please stop engaging with him by sending info about depression. You will regret prioritising his feelings & feel like a mug for doing so in future.
Depression does not make you forget you love people. You can feel not good enough & they would be better off without you, or that you’re a loser who doesn’t deserve them, but you don’t just walk out of your marriage because you’re depressed & want to find yourself. if it was real depression you would have seen him deteriorate & noticed signs earlier, probably having to ask him to either leave to sort his head out or go to counselling & often the fear of losing your family is what gives people the urge to seek treatment.
He has blindsided you. He may indeed feel depressed because he is not happy, but that is not the same as having depression. Him calling it that is a cop out to those of us who do have depression!
I would be almost certain there is someone else he has his eye on, even if it is not actual cheating, the statistical likelihood of this is too great to ignore. To up & leave suddenly, no talk of counselling or trying to work through issues makes it a lot easier to have that fling, because you are separated.
He is having his cake & eating it too because you’re sat here worried about him, while in all likelihood he is on tinder or talking to a colleague. Am sorry, know that’s difficult to hear but I would advise going to Chump Lady website - she will teach you how to stop doing the “pick me” dance which is what you’re doing right now.
If I were you would be seeking legal advice to ensure you get everything you’re owed.