You may love Chris Messina as Danny Castellano on The Mindy Project , but you're about to hate him in a major way. He stars alongside Glee's Dianna Agron  in the music video for Sam Smith's "I'm Not the Only One," and he's a huge cheater. The song itself is beautiful, but the video is really fantastic. The two have what looks like the perfect marriage, until he leaves the house and goes trolling for hotties at a bar. Agron's reaction is heartbreaking and unexpected — watch and see.