Katy and John had gotten quite serious but things weren't too pleasant between them lately, according to Us Weekly.
The two had been "fighting" lately, says a source, which added to the difficulty that had already been caused by their busy work schedules.
On March 22, three days after the news of their split broke, Katy took to Twitter to post a song by Tristan Prettyman called "I Was Gonna Marry You."
"Perfectly put," Katy wrote about the song.
They spent time with each other's families around the holidays, which may have caused some issues.
"Introducing her to his dad was a big deal," a source close to John Mayer reveals.
"It was just too much, too soon," another source adds.
Still, there's always a chance they could work things out yet again.
"They've broken up before, so it's hard to tell," a source says. "She's changed a lot since she's been with him... [you] can't argue that she has been in love."
At least for the time being, they'll both have to find other people to spend their Friday nights with.
Source: Us Weekly, Twitter