THEY MADE IT THROUGH RICHER and poorer, through sickness and health. But for Olivia Newton-John and her husband of 10 years, Matt Lattanzi, till-death-do-us-part proved one vow too many. Last week—having bounced back from the bankruptcy she declared in 1991 after her Koala Blue line of clothing went under and having recovered from the breast cancer that afflicted her in 1992—Newton-John gave word that her marriage was ending. Said a statement released by the couple on April 24: "[We] regretfully announce an amicable separation."

Some friends and family members saw the rift as inevitable. From the moment Newton-John, now 46, and Lattanzi, 36, met on the set of Xanadu in 1979, they were an odd match. She was the daughter of a British professor of German literature; he was the son of a maintenance foreman from Oregon. She was the recording star who helped make Grease the second most successful musical film ever (The Sound of Music ranks first); he was an unknown backup dancer. And though, at 31, Newton-John was well into adulthood, Lattanzi, at 20, was barely old enough to order a drink. After 15 years the union between Lattanzi, whose idea of fun is to fish, scuba dive and hang out with the boys, and Newton-John, who prefers to meditate and sip herbal tea, was, as a mutual pal puts it, "like trying to fit a square peg into a round hole."

Ironically it may have been Newton-John's cancer that kept the couple together this long. By all accounts, any difficulties between them vanished as Lattanzi tended to his sick wife. "He was so supportive of her," says Newton-John's niece Tottie Goldsmith. But with her recovery after a partial mastectomy came an acute awareness of their differences, which several months of recent couples therapy could not resolve. "The people she chooses to mix with now are very spiritual," says Goldsmith. "She needs to find her equal."

Earthly matters also need to be addressed. Neither the division of their assets (including homes in Malibu and Australia) nor custody of their 9-year-old daughter, Chloe, have been worked out. And while no one foresees animosity, no one predicts a reconciliation either. "Sometimes," says a friend of Newton-John's, "there is no putting Humpty Dumpty together again."