Spoiler alert, bitter woman alert, etc.
Celeste is a high-powered career girl, and Jesse's career involves surfing and sleeping off hangovers. It worked fine when they were in college, but now Celeste is reconsidering spending her life with an unmotivated loser.
She breaks it off and makes a lame foray into the world of singledom. She then realizes that in 2012, most men are emasculated, freeloading shmucks, and she eventually decides that she'd rather be with a loser she loves than some random loser, or no one at all. However, several weeks have passed, and Jesse has already managed to impregnate a hapless foreign girl.
