The actors, who began dating in early 2011, reportedly ended their relationship in recent weeks.
According to US Weekly, Roberts did everything possible to distance herself from the Glee star before the romance was officially over.
"Emma told Chord he didn't need to spend New Year's with her. It was just her and her girlfriends, a tradition she always does. Emma is pretty difficult to be in a relationship with," a source told the publication.
"Emma calls him Chord - pronounced like chair - to his face. She acts like he's really dumb."
However, a separate insider offered a different perspective, saying: "Chord was controlling and always wanted to know where she was at all times. Emma's career is very important to her, but Chord wanted it to be all about him.
"She's too young to be able to give someone that kind of commitment."
Roberts recently announced that she would defer her enrollment to Sarah Lawrence College in order to satisfy "work commitments".