Just while she vowed to start 2010 right did Lindsay Lohan discover that she was betrayed by no other than her sidekick.

The 23-year old starlet’s longtime bestfriend Patrick “Pootie” Aufdenkamp had apparently ripped her off by stealing her sketches for her 6126 clothing line.

According to a source close to LiLo, Aufdenkamp is now trying to do his own fashion line, and is off to debut his own collection using her designs this February 18 in NYC. He used to frequently accompany the actress in her various fashion-related work. The two had been best friends since she was 16.

The source adds: “It’s horrible. He was her best friend. He has always used her, and she’s been warned to never trust him. Lindsay is a good friend and likes to see the good in people. She didn’t want to believe how bad Patrick’s energy was, and how false his friendship has always been with her.”

As for LiLo, she just noted that her 7-year friendship with “Pootie” has come to an end. “I should’ve known better. But new year for me and a new beginning! Health, happiness, success and love!”

Photos by Wenn.com