Marjorie Alexander, 43, was discovered at a motel in Long Island with a plastic bag taped over her head. Several suicide notes were found.
Ms Alexander went public about her affair with Gotti, brother of the late mafia boss John Gotti, in the New York tabloids last week. "I did not fall in love with the wrong guy," she told the New York Daily News. "I am proud of loving him."
Gotti, who was convicted last year of trying to extort up to $3m (now £1.6m) from the film star Steven Seagal, was by all accounts in love with Ms Alexander.
"I can tell you Peter Gotti was very much in love with her," his lawyer, Gerald Shargel, said. "And this is devastation beyond words for him."
A mistress is an essential accoutrement in the macho mob culture. "It's just a certain style, it goes with the watch and the car," the late mafia boss Paul Castellano said. But such a lifestyle comes with responsibilities.
When Ms Alexander went public, speaking to the press and writing letters to the judge overseeing the racketeering charge that could put Gotti behind bars for 15 years, she violated the code.
"If ever a man doesn't belong in a family with such an infamous name and reputation, it is Peter," she wrote to Judge Frederic Block last year. "I know Peter for 14 years, now. No one on this earth is closer to him than I."
Gotti's wife Catherine was resentful of the affair. She also wrote to Mr Block asking him to impose the stiffest sentence possible on her husband. "His self-serving greed and philandering has put him where he is and deserves to be."
By Monday this week Ms Alexander was having second thoughts about making her affections so public. "I took a chance," she said. "Now I'm destroyed."