Former friends, staffers, and artists from Sean “Diddy” Combs’ Bad Boy label have come forward to claim the music mogul has a disturbing history of abusive and violent behavior that was Hollywood’s best-kept secret until recently, RadarOnline.com has learned. Sources close to the famed record executive claimed that his conduct had already begun during his college days when he allegedly beat his then-girlfriend with what appeared to be a belt in front of other students. An eyewitness told Rolling Stone in a shocking exposé published Wednesday following a six-month investigation that he was “scr…