Christina Aguilera's Boyfriend Matt Rutler "Happy" With Her Curvier Shape

Matt Rutler and Christina Aguilera attend a basketball game between the Oklahoma City Thunder and the Los Angeles Lakers at Staples Center on March 29, 2012 in Los Angeles, California. Credit: Noel Vasquez/Getty Images

Still going strong!

When Christina Aguilera, 31, started dating Burlesque set assistant Matthew Rutler in late 2010, "we thought it was going to be a quick, seat-of-your-pants romance," a Rutler source admits to Us Weekly.

But more than a year later, "it's turned into something special," the source shares. Credit that staying power to Rutler's eagerness to please his girlfriend of over a year--especially when it comes to the Voice coach's son, Max, 4. (Aguilera split from Max's dad, her ex-husband Jordan Bratman, in 2010).

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"He recently surprised them by taking them to Cirque du Soleil's Iris show," a pal says of Rutler. "They had a blast."

More recently, Aguilera threw Rutler a 27th birthday bash at burlesque-themed hotspot Le Descarga in Los Angeles April 5.

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"There were about fifty people there," a partygoer tells Us. "It was intimate! , and lo w-key. Matt and Christina were super affectionate."

Aguilera--whose figure has come under scrutiny ever since she first stepped into the spotlight in 1999--has, in recent years, been criticized for her curvier appearance. But none of that matters to Rutler: "Matt is happy with the way she looks, however it is," the insider shares. "Even when she was looking heavier, he would always say, 'She looks gorgeous to me.'"

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Earlier this year, the Grammy winner opened up to Marie Claire about the positive effect Rutler has on her self-esteem.

"I've been through my highs, I've been through my lows; I've been through the gamut of all things in this business," Aguilera shared. "Being too thin. Being bigger...It's noise I block out automatically. I love my body. My boyfriend loooooves my body. My son is healthy and happy, so that's all that matters to me."