Celebrity couple Cindy Crawford and Rande Gerber are the first to admit that marriage requires effort. "It takes a little bit of work, but if you're friends first, it makes [it] so much easier," Rande, a nightlife and spirits entrepreneur, has said of his relationship with his supermodel wife of 20 years. "We both know what our priorities are, and we work really hard."

Cindy and Rande are facing their toughest test yet. The parents of Presley, 19, and Kaia, 16, are on the rocks after two decades as husband and wife, an insider recently told In Touch in the magazine's latest issue, on newsstands now. "There has been constant drama in their marriage for years," the insider said of Cindy, 52, and Rande, 56, who have mostly clashed over cheating rumors.

Now, with their kids getting older and establishing modeling careers of their own, the pair are drifting apart. "Put it this way: They don't keep tabs on each other anymore. Sometimes it seems like they're living separate lives," the source shared.

cindy crawford family

Cindy has been known to obsess over Rande's ladies' man reputation. "He's a big flirt, especially when he was more involved with his nightclub business," the insider revealed. "Women were hitting on him all the time." In 2004, former W hotel waitress Harmony Kubiak claimed she and Rande made out and nearly had sex in 2000 β€” just two years after he wed Cindy. "It was a shock to Cindy when she heard that," the source explained. (Rande has denied affair rumors.) "Everyone thought she'd leave him, but she stayed."

Cindy's rep has insisted that "there are no problems in Cindy's marriage, nor is anyone fearing they are going to separate." But several years ago Cindy consulted a psychic, the insider said, because she "felt like her marriage was crumbling." Instead of ending things, Cindy decided on couples therapy, the source confessed. "She likes to say she's older now so she doesn't listen to the rumors, but she still worries." And she'll never forget.

Though the insider said the co-founder of the Casamigos tequila brand β€” which Rande sold for $1 billion last year β€” parties less now that his BFF, George Clooney, is a married dad, Cindy often "guilts Rande" about his wild past. The insider added, "He just takes it." But he might not for much longer.

According to the insider, the pair are waiting for Presley and Kaia to fully leave the nest before making any decisions about the fate of their marriage. "It is," said the insider, "a complicated relationship."