Celebrity doesn't always lead to security, a point hammered home yet again by tennis ace John McEnroe, 43, in his new autobiography "You Cannot Be Serious," which is being excerpted in the new issue of PEOPLE. Meeting his future wife at a 1984 party where, McEnroe admits, every guest was famous, "I went over and introduced myself, even though no introductions were needed. I knew very well that Tatum O'Neal had been the youngest person to win an Oscar, in 1974, for 'Paper Moon.' I was all too aware that her father was Ryan O'Neal, the Tom Cruise of his day . . . Was I overly impressed? A bit star-struck? Maybe," he writes. "Maybe Tatum was too." McEnroe candidly reveals problems that rocked the marriage, which was not helped by the birth of the couple's three children. Drugs and career slumps abetted the collapse of the union, he writes, as did the simple fact that "she compared all men to her father." The two divorced in 1992, and the three children -- Kevin, 16, Sean, 14, and Emily, 11 -- now live with the athlete and his second wife (since 1997), singer Patty Smyth, 44, and Smyth's child from a former marriage as well as McEnroe and Smyth's two daughters. "To me, the ultimate Is sitting around a dinner table and it's just all of us there," McEnroe tells PEOPLE, which reports that the onetime Super Brat of the courts owns a Manhattan art gallery and is doing tennis commentary for the USA network while he contemplates his next professional move. "I'm still the same person," he says. "But I'm trying to smooth out the edges."