The 35-year-old The Madden Brothers star, who is dating Diaz, hated seeing her get intimate with co-star Jason Segel on the big screen, reported OK magazine.
"Benji thought 'Sex Tape' was funny, but he admitted it was really tough to see her with another guy," a source said.
The former Good Charlotte rocker wants his 42-year-old girlfriend to start pursuing more serious roles that won't make him 'squirm'.
"She thinks he's being silly but is actually touched that he'd get jealous," it added.