In an interview with Life & Style magazine, the former tabloid reporter said the pair would sneak around the kids to have sex and shacked up in a New Jersey hotel room during their first night together.
"It was all pretty much sexual," Majors confessed to the magazine.
"That's what he had in mind. I'm deeply upset by the turn of events. He totally screwed me over and acted like a dirtbag."
Major, who said she resigned from her job at Star magazine because she fell for Jon, revealed details of their short-lived fling and said she fell hard for the divorcing father of eight and star of "Jon & Kate Plus 8."
"Jon said he couldn't be seen having a girlfriend, so he told me to drive to a neighbor's house after midnight, when the kids were asleep," Major told the magazine. "He said he'd pick me up on his four-wheeler, take me to his house and drop me off again at 6 a.m."
"I was shocked and said, 'No, I don't feel right doing that. What if the kids wake up?' He was like, 'They're not going to notice, they're not going to see anything.' He wasn't nervous about it -- I was."
Still, Kate was wooed by the unemployed octodad and gushed about their love life.
"He was a great kisser," she said. "It was amazing. I said, 'I've never felt like this about anybody else in my life,' and he said, 'Me too.'"
Major said the pair holed up in a New Jersey hotel room in mid-July and shared an intimate night together. That's when he told her he was no longer interested in 22-year-old Hailey Glassman, the daughter of his soon-to-be-ex's tummy tuck surgeon with whom he'd been linked to in the past.
"Jon never wanted to use his credit card -- he was worried that he'd get caught or spotted," Major said. "On July 20, we went to a hotel in New Jersey. I paid for the room, and he snuck up a back way. that was the first time we slept together.
"He said he was falling in love with me. He said, 'I thought Hailey was perfect until I met you.'"
The two were photographed dining out in Manhattan and hobnobbing in the Hamptons, but Major said the pair had planned additional trips but he invited Hailey instead.
"Even when we were in the Hamptons, we were planning to go to LA together to meet with Christian Audigier about Ed Hardy stuff. We also talked about going ot Las Vegas. Now he's taking Hailey -- and that was a trip we had planned together."
Jon left for Massachusetts on June 23 and shut off his phone, she said. When Major was finally able to reach him, he said he wanted to be single. He also sent her a text that read: "Do not contact me again."
Gosselin announced on June 22 that he and his wife of 10 years, Kate, had filed for divorce.