Chris Brown‘s ex-girlfriend is not buyin’ that Chris is “just friends” with Rihanna … telling her people that  she’s convinced they were having sex behind her back.  According to TMZ  people connected to Karrueche Tran … says that she feels betrayed by Chris because he  promised her that she was the only woman in his life … especially when she probed him about his feelings toward Rihanna.

We’re told Karrueche had suspected something was up between the two of them for weeks because Chris was acting differently — going to clubs alone, acting distant and ramping up his public appearances with Rihanna. Sources say Karrueche told friends she truly loved Chris … and felt that the relationship was great until Rihanna let Brown back into her life.  KARREUCHE GIRL! you was SO busy tweeting “ray charles to the bull” Chris was cozing up to any and every ho he wanted too. Is she slow? The world can see your relationship coming to an end before you did.. Did she not listen to the lyrics to “She Ain’t You”?