I'm with Her - Season 1 Episode 11 The Heartbreak Kid
Overview: Alex is a bit surprised when Patrick doesn't invite her to accompany him to his and Stevie's high school reunion. After overhearing a phone message from Laura — Patrick's high school flame — Alex begins to suspect that her mild-mannered boyfriend may be trying to hook up with his ex, and has to figure out a way to keep an eye on him during the party.