"It was embarrassing, it was humiliating," Rihanna tells Winfrey, 58, via an excerpt released Thursday to ABC. "I lost my best friend. Everything I knew switched, switched in a night, and I couldn't control that."
The 23-year-old performer got into a physical altercation with Rihanna the night before the 2009 Grammy Awards in February. He pleaded guilty to assault and was sentenced to five years probation, community service and one year of domestic violence counseling.
"It became a circus and I felt protective. I felt like the only person they hate right now, is him. It was a weird, confusing space to be in," Rihanna says while fighting back tears. "As angry as I was, as angry and hurt and betrayed, I just felt like he made that mistake because he needed help ... and who's going to help him?"
"Nobody's going to say he needs help," the "We Found Love" singer explained to Winfrey. "Everybody's going to say he's a monster without looking at the source . . . and I was more concerned about him."
Rihanna's interview on Oprah's Next Chapter airs Sunday, Aug. 19 at 9 p.m. EST on OWN.