"Every second it's a blow-up and then full on in love," the insider said, adding their busy schedules are adding to the tension. "She's touring and working her ass off, and he's working his off in the studio."
Rihanna, 25, and Brown, 23, have been dating on and off for about five years.
UsMagazine.com said Rihanna hinted in a Los Angeles concert Tuesday their relationship might be on the rocks again.
"How many of you are in love? How many of you hate love? How many of you don't [expletive] understand it?" she asked the crowd. "I'm in that group. The confused group." She then sang her hit "What Now."
Brown was ordered to complete 180 days of community service as part of his plea deal stemming from his 2009 assault of Rihanna. He was also placed on probation for five years and ordered to attend an anger-management program.
Brown and Rihanna confirmed last year they had reconciled after their headline-grabbing altercation.