Jessica Simpson’s friends ‘horrified’ by John Mayer’s 2007 Perez Hilton lip-lock

Jessica Simpson’s friends thought that John Mayer betrayed her when he made out with Perez Hilton — but she glossed over it because she was “head-over-heels” in love with the singer, we’re told.

Gossip blogger Hilton wrote about the 2007 incident in his new memoir, claiming that he ran into Mayer and Simpson at a New York club — when Mayer almost immediately stuck his tongue down his throat.

But an old pal of Simpson’s tells Page Six that there was more to the tale. What made the incident so shocking to insiders, they said, was that Simpson’s camp was locked in a war with Hilton at the time because he wouldn’t stop calling her “Jessica Simpleton” on his phenomenally popular blog — and referring to her little sister Ashlee as “Asslee.”

“Her friends were horrified” by the saucy smooch, said an insider, “but she didn’t care. John couldn’t do anything wrong, as far as she was concerned. She was absolutely head-over-heels in love with him.”

In fact, the insider said that Simpson probably marveled at the move, thinking that it would ingratiate the couple with the then-powerful blogger.

Hilton writes in “TMI: My Life in Scandal” that after co-hosting MTV’s New Year’s Eve celebrations with Christina Aguilera, they both hit a club in Chelsea.

He said that they ran into the musician couple, and Mayer told Hilton, “I like to watch gay porn, you know,” adding, “My favorite porn star is Brent Corrigan. He really turns me on” — and then he kissed Hilton.

Hilton recounts that Simpson seemed mortified and covered her face with her tresses. He said that Mayer then sat back with a “satisfied” look on his face and turned to gaze affectionately at Simpson, who “didn’t seem to know whether she was incredibly embarrassed or really turned on.”

A rep for Simpson declined to comment, and a rep for Mayer didn’t get back to us.