I never suffered from depression, but my ex-partner did (a few years ago). He was diagnosed with dysthymia, you could see it as a chronic depression. He was on heavy meds for a while because it got really bad. The meds helped him a lot and when he got better, our relationship was just not the same. I guess I had become more a counselor than a girlfriend, I didn't have a role anymore. At the end of it all I was so exhausted, I stayed single for 3 years!
But he's doing much better now, it's all that matters.
In his case it would definitely come and go, some days were better than others. It's hard to get rid of it completely, but what's important is that you know the signs and you know when/where to get help, which seems to be your case. Good luck, and you can come here anytime to tell us how you feel!