My Girlfriend's Boyfriend is a romantic comedy that follows the ups and downs of Ethan and Jesse, a young couple. In the beginning of the film, Ethan meets Jesse in a coffee shop. He is immediately taken with her, and asks for her number, which she gives him. However, moments later, Jesse meets another man, named Troy. Troy asks for her number as well, and Jesse also decides to give it to him.
Jesse begins dating both men, but does not tell Ethan that he is being cheated on. Ethan, meanwhile, is struggling with his career. He is a novelist, but has yet to be published, and is still getting over his last rejection. When he begins dating Jesse, though, he also begins writing a new story.
Soon, Ethan falls in love with Jesse, and it seems that Jesse also cares deeply for Ethan, even though she is also dating the wealthy, suave Troy. As Ethan draws closer to the end of his book, he makes the big decision to ask Jesse to marry him. Jesse, however, is struggling over the secrets she is keeping from Ethan and must decide whether to tell Ethan, or to leave.