An apologetic Boston Celtics forward Jared Sullinger is free on $5000 bail after he was arrested yesterday on charges of assaulting his longtime girlfriend last weekend after she “found evidence on his cellphone that he was cheating on her” Waltham cops said.

Sullinger pleaded not guilty in Waltham District Court yesterday to assault and battery destruction of property of more than $250 and witness intimidation.

“The experience was humbling and embarrassing for me” Sullinger said in a statement. “Yet I know that this situation has brought both sorrow and embarrassment to my girlfriend my family the Boston Celtics organization my teammates and my fans. To all of you I apologize from the bottom of my heart.”

Sullinger 21 assaulted his 23-year-old girlfriend of more than two years as they argued and she started packing her bags at their Waltham home Saturday morning Waltham police said. Police said Sullinger — listed as 6 feet 9 inches tall and 260 pounds — pushed her onto the bed and pinned her down then shoved her off the bed and would not let her up.

When Sullinger’s girlfriend told him she was calling police he grabbed her cellphone police said. She later found it smashed in another room the report said. Sullinger then left for a pre-scheduled flight to Ohio police said.