Sean “Diddy” Combs’ ex-girlfriend Cassie has been “cooperating” with authorities investigating the hip-hop mogul months after the former couple reached a settlement, RadarOnline.com has learned. Insiders said the singer is believed to be among the witnesses that the feds have been in contact with as they build their case. It is speculated that Cassie may have helped authorities establish probable cause to get a judge to sign off on the search warrants. Other women who sued Diddy have also been in contact with authorities, according to a new report following the raid of his Los Angeles and Miam…