Rihanna and Chris Brown had a "volatile" relationship before this weekend's alleged assault, an insider tells Us Weekly. A close friend of Rihanna's saw visible bruises on the singer's neck in December. "She told me, 'We broke up again,'" the pal recalls. "I didn't pursue the issue further." Meanwhile, things keep going downhill for Brown, 19, since the altercation the night before the Grammy Awards: two of hip-hop's biggest stars, Jay-Z and Kanye West, have come out in defense of Rihanna; his rented Lamborghini was impounded; and his Valentine's Day gig was canceled. Brown's sister says that he "is coping" after being released on a $50,000 bail on Sunday night.