If you have an emotionally abusive partner, and don't do something about it, perhaps depression is acting as a prompt for you to take action. Some part of you (your soul, say) knows better, and via pain (depression) is trying to shift you towards a better, more joyful, result. I believe we have an innate guiding system, and that this is how it works - move away from pain, towards joy.

You can fail to take action, you can take drugs to manage the negative situation more comfortably, but, if abuse is the underlying issue, a genuine change of circumstances is required.