The 52-year-old singer first began dating Richards in 2006, shortly after his marriage to Heather Locklear collapsed. Richards, 41, had also separated from her ex-husband Charlie Sheen, reported Ace Showbiz.
The couple subsequently split, but reunited last year and confirmed their new relationship status at the red carpet of the 12th Annual Golden Heart Awards here last month.
However, they fell out before the CMT Awards in Nashville last week, breaking up for the second time.
"It's over. They had an epic argument in Nashville and Denise told Richie she couldn't continue the relationship any longer," a source said.