Rihanna & Chris Brown Dangerous Love?

The night before the Grammys, Chris Brown and Rihanna joined the music industry’s elite at producer Clive Davis’s annual gala appearing—for a while, anyway—to be the smiling supercouple everyone has come to expect. “At first they were all lovey-dovey,” a witness says of the pair, who were with Brown’s mother. But an observer says that over the course of the evening, something began to change. “He was being cold to her,” says the source. “He was getting annoyed.” The tension mounted when the couple were leaving the Beverly Hilton around midnight, as Rihanna stopped to chat with Miley Cyrus, Taylor Swift and Katy Perry. “He grabbed her hand, like, ‘Come on, let’s go,'” says the witness. “He wanted to get out of there.”

What happened next remains murky, but this much is clear: For the couple, this year’s Grammys will be remembered for all the wrong reasons. Driving in a Lamborghini, Brown, 19, and Rihanna, who turns 21 on Feb. 20, ended up in the quiet Hancock Park neighborhood of L.A. According to the police, who did not name Rihanna (real name: Robyn Rihanna Fenty), a 911 call was made reporting a disturbance. By the time the cops arrived, Brown was gone, leaving behind a visibly injured woman who sources say was Rihanna. She identified him as her attacker. “Chris knocked her around,” says a friend of the couple. “Black eye, blood, bruises. She had to be treated by a doctor.” Reached by PEOPLE, her rep simply said, “Rihanna is well. Thank you for your concern and support.”

The pair, both nominees who were each scheduled to perform at the Feb. 8 Grammy ceremony, were no-shows at the dress rehearsal early Sunday morning, but it wasn’t until around 1:30 p.m. that producers got a call that neither would be attending. Shortly after the Recording Academy released statements confirming the absences, Brown turned himself in at a Los Angeles police station, where he was booked on a felony charge of making criminal threats and released on $50,000 bail. As the Grammy show got underway, attendees buzzed about the missing couple. “It’s scary,” winner Estelle told PEOPLE. “I just pray that everything is all right.”

A source in Brown and Rihanna‘s circle says the couple’s relationship had been rocky for a few weeks: “They’ve been fighting a lot lately. Lots of ups and downs. One second they’re all lovey, and then they’re fighting like crazy.” Still, the news stunned fans and friends alike. Brown, known for his charm and Michael Jackson-style moves, has always been seen as a good kid. “I’ve never known Chris to be combative,” says his high school gym teacher from Tappahannock, Va., Lyn Amos. “He’s always low-key, easygoing.” Adds Jean Segar, a retired restaurant owner who has known Brown since he was a child: “He’s such a mild-mannered person. It’s hard for me to believe [the charge].” What makes the allegations even more shocking is that Brown has claimed his mother was physically abused by his former stepfather. “He made me terrified all the time,” Brown told Giant, adding, “I hate him to this day.”

In the lead-up to the Grammy weekend, Brown and Rihanna—who have always been tight-lipped about their romance—appeared typically carefree and affectionate. On Friday, during rehearsals for Sunday’s telecast, one source says they were “sweet with each other.” Adds another: “They were all over one another.” That same night they attended a bash where Rihanna performed and Brown mingled with Diddy and Paris Hilton. Says a source: “They looked like the perfect couple.”

It’s been that way ever since the pair, as Rihanna has put it, became “verrrry good friends.” They first became pals in 2005, and a romance blossomed last year, after Brown pursued the Barbados-bred beauty, a Jay-Z protegé who skyrocketed to fame with the ubiquitous hits “SOS,” “Don’t Stop the Music” and the Grammy-winning “Umbrella.” Since then, they’ve been inseparable from L.A. to New York and through Europe, Australia and the Caribbean. Says a music insider who knows Brown: “They never had public spats.” In fact, Brown said his attraction to Rihanna was due to her laid-back nature. “She’s down-to-earth, real cool,” he told PEOPLE in August, though at the same time, he shot down rumors they were house-hunting together. “I’m 19! I barely want my friends to stay over more than three days.”

Indeed, a source calls Brown “really immature. He’s the type of guy that would keep splashing you in the face in the pool if you were just trying to chill.” The fact that both stars are so young—and so famous—makes the relationship tough, says a source who knows them. “Plus, it’s inevitable that they will fight because they are together so much.” Also an issue: “She hates when he talks to other girls, and a lot of their arguments stem from her jealousy,” says another source. But Rihanna told radio host Ed Lover last year that it’s impossible to be angry with Brown: “You can’t get mad, actually, because he is just hilarious.”

The current state of their relationship—not to mention Brown’s career—is no laughing matter. Wrigley’s has temporarily suspended his Doublemint commercials, and as an industry source points out, “A lot of his fans are women.” Brown, who hired criminal defense attorney Mark Geragos (he defended Scott Peterson), is due in court March 5 and could face more charges from the district attorney. The case also rides on how much Rihanna (who is in a “safe place,” says a friend) can forgive. “Prosecutors back off somewhat when they see a couple trying to work out their own issues,” says Steve Sitkoff, an L.A. defense attorney. But, says the friend, “I would be so sad if she went back to him.”

If convicted just on the original charge, Brown faces up to three years in prison. And he’ll have to work hard to restore everyone’s trust. Says his former classmate Trina Reynolds: “I know his mama taught him better than that.”