They enjoyed a romantic lunch together to celebrate Mayer's special day and Perry, 27, was hoping to get more serious with him before their most recent split, reported the New York Daily News.
"She's been really depressed and needs attention. She really liked him and thought it was going to be something serious," a source said.
The couple, who first started dating in June, were also seen having dinner at Pearl restaurant in the city before going clubbing together on Sunday night.
Their latest reconciliation comes just days after Perry had grown tired of Meyer's failure to commit.
"John liked Katy, so he wanted to keep her in his life, but it just wasn't up to Katy's standards. She needs the guy to be on board 100 percent and she was sick of John disappearing for five days at a time, then booty calling her, then straightening up and treating her well, only to go back to his old behaviour a few days later," the source added.