Ptak has given you wise advice. I would only add that you sound like you need a little break from the pressures and responsibilities of even a very good relationship, in order to figure out what else you need/want to do to get better. Maybe you need a bit more space and time to regain strength and perspective? So the decision is probably not so black and white, whether to break up. If I were you, I would put off any such decision, and just take some time for yourself, which may include counseling and/or other possible forms of help. Your girlfriend of this long a time likely has some understanding of depression by now and would hopefully understand your need to focus more directly on your difficulties and possible solutions.

I am new here, but am an older person and not at all new to depression. And I still struggle with it. But there was a time two years ago when I nearly felt ready to leave my husband for reasons similar to what you describe, and a 10-day break, to be by myself, helped clarify for me that that wasn't the answer. It was not an easy 10 days by any means, and your own answer to such a question may turn out to be different, but sometimes a little space and time can help, one way or another.