Actually, he really doesn't. There is no do ented history of this at all. The only evidence that he has had any depression issues is the one-line social media post he made saying "This depression got the best of me". He got all kinds of positive support for that, so he later offered more info saying that he has his ups and downs and no matter how strong a pro athlete seems they have their days too.
That's it.
So yes, Demar has admitted he has better days and worse days, but that's not a diagnosis of clinical depression or something. He's a little bit fragile mentally for someone who's supposed to be a star athlete, so he probably struggles with that, but prior to that little message all everyone heard about Demar was how hard he worked how much of a gym rat he was, how motovated he was to get better every year, etc... and these aren't things that happen when someone struggles to gwt out of bed or can't cope with people or other signs of true depression. He was having troubles with his girl and was feeling emotional about it. Everyone gets depressed over things at times, but that is NOT the same as having a history of depression in the sense of the debilitating sort of depression that people get on meds for. It's not the same as being chemically imbalanced.
It's the pressure of being a highly paid professional athlete and being judged on results. Some people can handle it some people can't. If that makes them sad or makes them question themselves, that is NOT the same as true depression. It's no different than the temporary, normal emotions that no adult human escapes from when things aren't going their way, when they have job or relationship troubles, etc...
It has become a convenient excuse for his fans who aren't willing or able to accept that he's simply not as good as they think he is and to cover up his fragile ego.