The pair enjoyed a romantic candlelit dinner at the Sunset Marquis hotel in Hollywood on Saturday after she flew out last Thursday (09.09.10) to spend time with him.
One diner told the Daily Mirror newspaper: "They looked like the perfect couple. Derek couldn't take his eyes off Cheryl and she didn't stop smiling the whole night.
"They looked so into each other, it was like watching a couple of lovesick teenagers. They were being very tactile and flirty - they didn't seem to care who saw them.
"Derek was being a true gent and treated Cheryl like a princess. He even pulled her chair out for her as she got up to leave before they slipped off quietly through a back exit."
Cheryl split from her soon-to-be ex-husband Ashley Cole earlier this year after it was claimed he had cheated on her with numerous Women, and professional dancer Derek has supported her throughout her pending divorce.
Derek's dancing co-star Karina Smirnoff has also spoken out about how happy Cheryl has made her pal.
She said: "Derek is so in love. He's the happiest he has ever been. He deserves to be happy, Cheryl makes him smile. He's been holed up from the minute she got here. We haven't seen him."
A source said: "Nadine desperately wants to be friends with all of her Girls Aloud bandmates, despite whatever's happened in the past and things that have been said. Nadine's been having fun with British celebs out in Hollywood who've told her life's Too Short to spend time worrying and getting upset."