Adrienne Maloof's split from her husband of 10 years may have come down to that classic clash between work and personal life.

After the Real Housewives of Beverly Hills star's husband, Paul Nassif, filed for legal separation Monday, citing irreconcilable differences, a source close to the situation tells PEOPLE, "The show was the killer. It was the straw that broke the camel's back."

Maloof and Nassif, who has appeared on E!'s Dr. 90210, became very competitive, adds the source. He "was into the fame of it. He was the one who encouraged her to do Real Housewives."

They "went head to head all the time," the source adds, as "Adrienne then became the Housewife with the storyline, and he was just the husband."

Still, the couple are both concerned about their children: 9-year-old Gavin and 6-year-old twins Christian and Colin. Nassif is seeking joint physical and legal custody of their sons, according to the filing in Los Angeles Superior Court.

"Adrienne is a really fierce momma bear," says the source of Maloof, 50. "The tension in the house was something that kids didn't need to hear. The split is the best thing for everyone."

With season 3 of the series scheduled to premiere in the fall, there's no telling what drama will play out on the small screen.

"It's not a surprise at all," adds the source. "They've been on the cusp of splitting for a long time."

Read more at http://www.people.com/people/article/0,,20616905,00.html