"Benji spends so much time at Cameron's that it seems he now kind of lives there. They look very happy together ... Cameron hasn't looked this happy for years."
Benji met Cameron's family during a recent trip to Florida and the actress was delighted to show off the rocker.
A friend said: "It seemed important to Cameron that Benji met her family, and she looked very proud to introduce him to everyone. They were very sweet to each other, constantly kissing and flirting. It was obvious that they had a great vacation."
Nicole Richie recently revealed she takes full "responsibility" for Benji and Cameron getting together.
The 32-year-old socialite - who is married to the former Good Charlotte rocker's twin brother Joel Madden - "approves" of the couple's new relationship and admitted she was the one who got them together.
Asked if she set them up, she said: "Yes. I'm going to take responsibility for everything!"
Nicole - who has children Harlow, six, and Sparrow, four, with Joel - is delighted her brother-in-law has found happiness with the Sex Tape actress in recent months.
She added: "I approve of anything that's going to make Benji happy.
"I am a devoted sister-in-law. I'm happy for anyone who is happy, and I want everyone to be surrounded with love."