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Engaged nine days after meeting and married just one month later – in a reality TV special, of course – Khloé Kardashian Odom and Lamar Odom have spent much of their nearly four-year marriage defying doubters. When they pulled the plug after two seasons on their E! series Khloé & Lamar a little more than a year ago, Khloé denied rumors of trouble, insisting that they had decided to "prioritize" Lamar's struggling NBA career. Her husband expressed his gratitude. "If she has your back, she's going to follow through," he told PEOPLE in April 2012. Instead rumors seemed to strengthen her resolve. "I'm protective of Lamar," she said. "I hold our relationship sacred."

She was protecting him from far more than anyone realized. While the pair weathered reports of his infidelity over the past several months, Khloé, 29, had a more pressing concern: Lamar's use of hard-core drugs, according to multiple sources close to the couple. Her famous family, who recently celebrated the arrival of sister Kim's baby North (see box), "thought everything was fine because that's what she told them," says a source close to Khloé with direct knowledge of the situation. Privately, however, "she's kept this secret for almost two years, trying to save Lamar and their marriage," says the Khloé source. "She's ashamed," adds another source in their circle. "She's scared."

An attempt at rehab last year failed when Lamar, 33, left after just a few weeks. But things reached a breaking point on Aug. 21, when Khloé – who "recently came clean" to family about Lamar's problems, the source close to her says – issued an ultimatum that he go back to rehab, which he refused. "To my understanding it isn't any one drug, really, but that's part of the problem," says a source who has known him for years. "Lamar doesn't think he has a specific 'addiction.' He says he likes to party but that he knows when to stop."

During the media firestorm that ensued, reports enumerated his alleged drugs of choice (everything from OxyContin and Ambien to crack) and claimed that the NBA star had gone missing for 72 hours, a charge his agent Jeff Schwartz dismissed. ("His wife knows exactly where he is," he told ESPN Aug. 26.) On Aug. 25 Khloé tweeted in frustration, "Really hard to sit here and listen to people talk s--- about my family ... I'm too protective for this s---!" Although they are living apart—Lamar has been staying at various L.A.-area hotels and his downtown pad while she bounces between the duo's Tarzana, Calif., home, her mom Kris Jenner's estate and the Four Seasons in nearby Westlake – they are "in touch," says the Khloé source. When reached by PEOPLE, Lamar's father, Joe, described the situation as "really hectic." How is Lamar doing? "He's doing okay," said Joe. "But it's been real serious." As for reports that the two have separated, "Khloé hasn't made any decisions yet about what to do [with their marriage]," says the source close to her. "Right now she's just leaning toward trying to get him help."

But Lamar's drug use isn't the only issue threatening the couple's marriage. The close source says Khloé believes that the troubled athlete – a free agent since his most recent contract with the L.A. Clippers expired last season – has been unfaithful. (Lamar has previously denied the allegations; his agent declined to comment for this story.) "Khloé has always known he has groupies, but she believes that when he's sober, at least she doesn't have to worry about that," says the Lamar source. "But that's another part of the drug use: When he's off the rails like this, there's no telling what goes down."

The New York City-born Lamar has already lived through his share of highs and lows. At age 12, he lost his mother to colon cancer; he has disclosed his father's battle with heroin addiction. In 2001 he was suspended from the L.A. Clippers for violating NBA drug policies twice in eight months. Admitting to marijuana use, he told the Miami Herald in 2003, "I just couldn't control myself in L.A ... A lot of times I'd think, 'Damn, am I fighting my father's demons?' " (An NBA source who knows Lamar says, "He was always a time bomb with off-the-court demons.")

He went on to win two NBA championships during his eight seasons with the L.A. Lakers, but his life was touched by tragedy again in 2006, when he and then-girlfriend Liza Morales lost their 6-month-old son Jayden to Sudden Infant Death Syndrome. (The ex- couple also have two other children: Destiny, 13, and Lamar Jr., 10.) Then in July 2011, Lamar was riding in an SUV that struck and killed a teenage pedestrian. The following February he disappeared from his then-team, the Dallas Mavericks, for 10 days. "It was really personal and something I had to tend to," he said later. Asked about Lamar's current problems, Mavericks owner Mark Cuban told PEOPLE, "I hope Lamar gets it figured out. That's all I can say."

Now Lamar's friends and family hope he will get the help he needs. "People are surprised Khloé's put up with all this, but she truly loves Lamar," says the source in their circle. The two had even been planning to renew their vows this fall. Now the future of their marriage is in question. "Khloé just wants him to get better," says the Lamar source. "She keeps thinking that he'll come to his senses and get help. But it hasn't happened like that."

  • Contributors:
  • Jennifer Garcia/Los Angeles,
  • Pernilla Cedenheim/Los Angeles,
  • Elizabeth Leonard/Los Angeles,
  • Aili Nahas/Los Angeles,
  • Gabriella Olya/Los Angeles.