Associated Press
Christie Brinkley

NEW YORK — Christie Brinkley, testifying Monday at her divorce trial, said it was a "nightmare" to put on a brave face and throw a birthday party with 30 kids after learning that her husband had an affair with a teenager.

But the model, who loves making birthday cakes, said such homespun family celebrations are part of a lifestyle that means the world to her.

"That's the only thing I've ever wanted," she said. "That's the most important thing — to have a big, happy family."

Brinkley, 54, described for the court a seemingly idyllic lifestyle: an old farmhouse, "full of life," brimming with children's music and art, and beloved pets.

She said she tried to spare her two young children the messy details of the breakup, including her discovery of husband Peter Cook's Internet pornography habits.

She told the children: "I think daddy has fallen out of love with me." But she assured them they would always be "very, very loved."

The couple married Sept. 21, 1996, following a whirlwind courtship of about five months.

Now, they are arguing over custody of the children, ages 10 and 13. Alexa Ray Joel, 22, Brinkley's daughter with "Piano Man" singer Billy Joel, is 22.

Last week, Brinkley testified that her world "was completely shattered" by news of the affair. "My life as I knew it had vanished."

The court also heard testimony last week from Cook, 49, an architect, and his former mistress, Diana Bianchi, who was 18 when she began seeing him. Cook said he gave Bianchi a $300,000 payoff, had trysts with her in his office and Brinkley's Hamptons homes, and spent thousands of dollars on online porn.

Brinkley said Monday that as the scandal became public, she took the children on a private plane for a vacation in Colorado.

"I took them to the top of a mountain and we camped out under the stars," without TV or Internet access, she said.

While they were away, she said, "Ms. Bianchi spilled the beans. She went on TV to get her 15 minutes of fame."

Under questioning from her lawyer, Brinkley said she had remained faithful to Cook. And, though she's divorcing, she's not interested in dating.

"I think the kids have been through a lot of changes," she said. "... I just don't think this is the time for that."