Prior to Kallie unraveling the truth about Gavin, she wants to prove to him that she is a loving girlfriend (by performing affectionate or romantic gestures). But in reality if Gavin truly cared about her, Kallie wouldn't have to substantiate anything. She already is his partner and all she's doing is the bare minimum. This inspires the title of the film for its 'Catch-22' plot point.
Gavin's appearance is out of view throughout the film on purpose. This was designed for the audience to insert their own betraying ex into the slot that is Gavin Moore, despite a conflict one is in (big or small).
