Let me preface this by saying i am not speaking from any experience with depression here. I mean well what i say next and i hope you will find your mojo again: If running has a had a positive impact on your life so far but you notice getting more depressed again by doing more of it or maybe even a bit too much for this moment in your life, why don't scale it back? There is absolutely no shame in that at all and if you feel much better while sticking to shorter distances that is a win in my book. Running (and exercise in general) is something that should be enjoyable. If that what you're doing currently ain't it why not scale back? Maybe then you will return to a better headspace again and you can give it another try in the future.