From Wikipedia:
It was announced on February 21, 2015, following his second suspension for marijuana use, that the Bucks were buying out Sanders' contract.[16] On February 25, a video of Sanders was released where he explained that he entered into a program at Rogers Memorial Hospital for anxiety, depression and mood disorders. He said that the program led him to realize "what's important, and where I would want to devote my time and energy" and that ultimately he realized that "for [basketball] to be consuming so much of my life and time right now ... it's not there for me. It's not that worth it." He did, however, claim to still love the game and that "if I get to a point where I feel I'm capable of playing basketball again, then I will."[17][18]
I don't think there's any evidence that Sanders was a bad guy, just that he had some problems, and he evidently recognized that and addressed them If his head is back in a good place, we could do a lot worse.