"It was my success as a celebrity reality star and notoriety that bothered him," Singer tells PEOPLE

Credit: Billy Farrell/BFAnyc/Sipa USA

When Ramona Singer filed for divorce in August, ending her 22-year marriage, she couldn’t believe what was happening. But after being blindsided by a cheating scandal, Singer had had enough.

With her divorce underway, The Real Housewives of New York star says she missed the signs leading up her husband Mario’s affair. She’s now opening up to PEOPLE about her divorce, which she chronicles in her book Life on the Ramona Coaster (out July 28).

“I think he felt that we were no longer a team,” says Singer.

As Singer became a full-blown reality star, Mario became increasingly resentful. “It was my success as a celebrity reality star and notoriety that bothered him,” she tells PEOPLE. “If someone said, ‘Can I take a photo with Ramona?’ or interrupted our conversation at dinner, he would get upset.”

Rather than voicing his concerns or becoming a more active part of Ramona’s fame, Mario remained silent.

“He could have jumped in but he continued to be passive,” says Singer.

This level of unhappiness came as a shock to those around the Singers, who often described them as the “dream couple.”

By the time Singer realized that her husband felt as though he had been put on the backburner, Mario had already begun an affair.

“The affair was really a symptom of unhappiness,” Singer tells PEOPLE. “It’s still betrayal.”

For more on Ramona and Mario Singer’s divorce and how she is coping, pick up this week’s issue of PEOPLE, on newsstands Friday