Maybe adults get bored in the summer and should go away to camp. Maybe it’s piña colada poisoning. Or sunscreen abuse. Whatever the cause, this has been a season of marital restlessness for some well-known celebrity couples. The three-year union of Bruce Springsteen and Julianne Phillips has unraveled, and the Debra Winger-Timothy Hutton marriage is on the rocks. Come Labor Day, there are certain to be some sheepish responses to that old question, How did you spend your summer vacation? The answer may be depressing, liberating or both for the following duos: Singer Lionel Richie, 38, and his wife, Brenda, 35, who were involved in a violent domestic dispute that shattered the nighttime calm of a Beverly Hills neighborhood; Princess Stephanie, Grace Kelly’s 23-year-old rebellious daughter, who ended a tempestuous 20-month affair with French-born gadabout Mario Oliver (né Jutard), 36; and San Francisco super-lawyer Melvin Belli, 80, who filed to divorce wife Lia, 39, and claimed that she has had numerous affairs during their 16-year marriage. (She denies the charges and complains that after a recent shooting attempt on her life in their home, Belli, who was away at the time, was more concerned about the fate of his four dogs than with his wife’s safety.)

And Labor Day is still seven long weeks away.

Velvet-voiced Lionel Richie didn’t have to ask, “Hello, is it me you’re looking for?” when his wife, Brenda, suddenly materialized shortly after 2 a.m. on June 29 in the Beverly Hills apartment of Diane Alexander, a friend of the couple’s. According to police, Brenda found her husband with Alexander and promptly drop-kicked him sharply in what everyone is delicately referring to as the “stomach area.”

Lionel left before police arrived but later telephoned authorities to say he had been assaulted by his wife. Brenda, meanwhile, turned her fury on Alexander, a 22-year-old model and dancer. When officers arrived, they found Brenda striking and kicking Alexander on the living room floor.

“They were screaming and you could hear everything,” said Francies Devinney, a neighbor of Alexander’s. “Lionel was there, and it was obvious that his wife had just found him with Diane. His wife was really, really mad. Glass broke and furniture crashed around inside. It sounded like she was killing someone. It wasn’t very civilized.”

Another neighbor, Gary Oropeza, 35, reported seeing Brenda kicking and fighting with police outside Alexander’s apartment. “They had to push her down on her chest on the ground to get the cuffs on her,” he said. “She kept screaming for Diane to help her; she kept screaming, ‘Diane, don’t let them do this to me. Please, Diane.’ ”

Alexander refused medical treatment, but Brenda was treated for a cut on her right ankle and returned to police custody. She was charged with corporal injury to a spouse, resisting arrest, trespassing, vandalism, battery and disturbing the peace. By 9 a.m. she was free, after posting $5,000 bail provided by an unidentified female friend. She’ll be arraigned on those charges on July 29 and could face several months’ imprisonment and/or a hefty fine.

Devinney says Lionel was a frequent visitor to the apartment: “He parks in the back and walks right by my window all the time.” One source claims that Richie has been seeing Alexander for several years. The two are believed to have met at the 1984 Olympics in L.A., where Richie sang and Alexander was among the hundreds of dancers who performed in the closing ceremonies. More recently she appeared in the video of his 1986 hit Dancing on the Ceiling.

Long one of Hollywood’s most attractive couples, the Richies have been having marital problems for about a year, according to one insider. A friend of Lionel’s says that the singer moved out of the couple’s Bel Air mansion and into a Malibu bungalow for several months last spring, then moved back in with Brenda four to six weeks ago. “It’s been pretty intense for the last year,” the friend said. “Obviously, things aren’t too good at home.” The vehemence of Brenda’s reaction surprised her friends, one of whom, Sandra Moss, described her as “very soft-spoken. She’s just the most adorable, caring, pretty, bright…. I can’t believe she did this.”

So far, no divorce proceedings have been announced. Nor, for that matter, is there any talk of a rematch.

The official story is that Mario Oliver, a playboy and part-owner of an L.A. nightclub, asked Princess Stephanie to choose between him and her singing career. She did—and chose her career. But according to one insider, Stephanie, too, arrived home to find a distressing situation. The princess recently returned earlier than planned to the Beverly Hills home that she and Oliver shared and apparently found Mario with 18-year-old Julie Royer. (A freshly minted high school graduate, Julie has frequently been seen on Oliver’s arm during the last three months.) Stephanie, not called Her Serene Highness for nothing, refrained from giving him a kick in the “stomach area”; she merely gave him two days to find other accommodations and ended the whole thing with dignity, just like a princess should. “It wasn’t a drama,” says Jean Miguel, Stephanie’s agent in Europe. “There were no screams or pain.”

Stephanie and Mario were never anyone’s ideal couple, especially not Prince Rainier’s, who had always refused to meet his headstrong daughter’s beau, a twice-married convicted sex offender. Insiders say that Grimaldi père, who was the first to hear the news from his daughter, was delighted at the turn of events. Indeed, Oliver told a French reporter that “the date of our separation will probably become a national holiday [in Monaco].”

The pair had been inseparable since they began living together in L.A. in October 1986, although skeptics insisted he was using her name and money to get publicity. Still, in all their months of passionate togetherness, there had been talk of marriage. Stephanie now attributes those discussions to youthful ignorance. “How can you know at 21 if love will last eternally?” she said recently. “Life sometimes decides otherwise.”

In an interview with Paris Match, Stephanie was forgiving toward Mario: “Let’s say we didn’t understand each other. I don’t feel any bitterness. I only want to remember the good times.” But he wasn’t at the top of her list when she was asked, “Who is the man you have loved the most?” Said Stephanie: “The only one who has never betrayed me—my father.”

Asked whom he loves the most, octogenarian barrister Melvin Belli would probably name one of his pet greyhounds. Far, far down the list would be his fifth wife, Lia, who filed for separation July 1, just four days after, she claims, a mysterious intruder broke into the couple’s San Francisco mansion and fired two shots at her. Lia says she suspects the hit man was hired by an unnamed family member intent on permanently cutting her out of Belli’s will. But the last straw, she said, was Belli’s reaction to the shooting. “My husband called his office [he was on vacation in the Soviet Union] and was told what had happened,” she says. “He only wanted to know whether the dogs had been harmed.”

When Belli got back to San Francisco on July 2, he was armed with his own ideas about who had taken a shot at his wife. Belli’s prime suspect is Alexander Montagu, Viscount Mandeville, the Australian-born son of the 12th Duke of Manchester. (Montagu later provided police with an acceptable alibi.) Lia did call the cops about the viscount back in April, after he pulled a knife on her at Michael Jackson’s L.A. estate. But she says now that she “overreacted,” and both she and Montagu, 25, deny they are lovers.

According to Alex, Lia took him under her wing when he was 7 or 8 years old. “I love her like a mother,” he says. “There’s no sex involved at all. That would be like what the Australians call grab-a-granny.”

Lia vigorously denies any sexual involvement with Montagu and, in a written statement to police, claimed that her husband’s charges of extramarital affairs—including liaisons with South African Archbishop Desmond Tutu, Zsa Zsa Gabor and the Bellis’ gay housekeeper—were wild and unfounded. “In 16 years of marriage,” Lia declares, “I have not had an affair with a man, a woman or a goat.” Belli, for his part, bleats that he never accused her of involvement with Zsa Zsa or Tutu.

Lia wants Belli legally barred from their mansion, where the couple had maintained separate, locked bedrooms. “I haven’t slept with her in a couple of years,” he says. She disagrees: “It’s much longer than that. It was made very clear that my husband was repulsed by me.”

Melvin, co-author of a new book, Divorcing, to be published next month, says he filed for divorce last week. A custody battle has also started. It isn’t about their daughter, Melia, 15, who is vacationing in London, but about Wheldone Rhump Roast IV, the Bellis’ Italian greyhound, which Lia is keeping, for now. (Melvin says he took the other three dogs.)

Alexander, the enigmatic viscount, says he’s suing too—for libel. “If I win this lawsuit and Belli can’t afford to pay me,” he says, “I am going to get his law buildings, and I’m going to paint them bright pink, and I’m going to turn them into public toilets.”

As for Belli, he’s looking forward to bachelorhood again. “I’m going to live with my dogs in peace and harmony and comfort,” he says. “At least they don’t steal and take my credit cards.”

—By Michael Neill, with Angela Blessing and Tina Johnson in Los Angeles and Dianna Waggoner and Maria Wilhelm in San Francisco and Cathy Nolan in Paris