. . . Aaron Carter!
You know you remember this one: teen stars Lindsay and Hilary were pals before Hilary and Aaron started dating in 2000 (they were just 13 years old). According to Aaron, they dated for "like a year and a half," before he "got a little bored" and began getting to know Lindsay. "Then I didn't want to do that anymore, so I got back with Hilary. And then I ended up cheating on Hilary with her best friend," he added in a 2006 interview.