From MTO: just got some STEAMING HOT TEA, from one of Chris Brown's MOTHER'S friends. She told it ALL . . . no filter.

According to Mama Brown's friend, the real reason Rihanna left him wasn't because of any female, but the fact Chris crew - who he refers to as OHB (which includes Kae) - are "not good people." According to her, Chris had a pretty bad DRUG problem (although she doesn't say WHAT drug). She explained, "He wouldn't get help for a drug problem, so she [Rihanna] gave him an ultimatum and left."

And Chris' mother is 100 PERCENT WITH RIHANNA. Mama Breezy and Rihanna have REMAINED FRIENDS for all these years. And they are in constant contact and Mama Breezy believes that Rih and Chris are "soul mates." Rihanna and Chris BOTH agree.

Chris' mother had enough last October, when Chris came to her home with his friends, and Karrueche, they completely disrespected her and he was high as a kite. She didn't know what else she could do for him, so she SUPPORTED RIHANNA in her ultimatum to Chris.

Luckily for them both, the COURT got involved and forced Chris into rehab. And the news is MUCH BETTER NOW. Since Chris has been entered rehab, he has completely turned things around. He's finally decided to CUT many of the OHB crew members out of his life. And he and Rihanna are MENDING their relationship.

According to our source Chris is 100 PERCENT trying to win Rihanna back. We're told that Rihanna has been visiting him "regularly" and the pair have decided that once Chris is released, the two can figure out what to do with their relationship.

As for Rihanna's relationship with Drake? Chris' mama's friend told us, "I think Rihanna is just trying to TEST Chris, to see whether he acts out over it, or whether he handles it well. That will prove to her whether he's really changed."