I'm going to break up with my girlfriend due to her depression.
Which comes first, the depression or the breakup?
It's a bit tricky, I have to give it some time for a definite answer. Depression led to the breakup.
I guess it depends on how much you love her. Depression can be worked through. Make sure you won't regret breaking up over something that could have been worked through.
I dated a whore so I deserve better.
It's kind to help a partner through a mental health issue. But it doesn't sound like you respect her very much, so it's probably for the best that you've broken up. It's not that nice, though.