KATY PERRY gave boyfriend John Mayer the heave-ho because she caught the guitar-slinging Lothario cheating on her…AGAIN.

“Katy finally had enough of John’s wandering eye,” revealed a close source. “He’s an incorrigible flirt who’s constantly chatting up other women, asking them for their phone numbers so he can text them.

“SOMETIMES, HE WOULD EVEN ASK them out for drinks, and Katy got sick and tired of it.”

The 28-year-old “I Kissed a Girl” songbird was first linked to the 35-year-old playboy last summer, less than a year after Katy and husband Russell Brand divorced.

It’s been a rocky relationship, and horndog John was recently rumored to be getting cozy with pretty “Girls” star Allison Williams, who is NBC newsman Brian Williams’ daughter and the girlfriend of a close pal.

They were spotted together at a Manhattan fashion event in late January, and that was just about the last straw for Katy.

“Many of Katy’s friends warned her that John couldn’t remain faithful, but she didn’t want to believe them,” said the source.

“They split briefly in August, but Katy gave John another chance and now he’s blown it.

“John has begged her to take him back, but Katy wants nothing to do with him anymore.”