oh boy...as an employer i can talk a lot about jobs, employees and of course, as a pc member, disorders.
quitting is never a good thing....i tell my people they don't have a job they have a career.
once they treat it as such, they tend to turn around a little...depression or not.
i have worked through three employees with clinical depression (2 successfully, 1 not) and give them what they need for support but also try to let them know their career can be the one grounding force in their lives and they would do very well to do whatever it takes to preserve it.
maybe you need a career change?