You go from concerned to all-out panicked. Despite the gentle protestations of your friends that perhaps he's just not that into you, you remain convinced that he was hit by a cab and rendered a cripple, and is too proud to leave his apartment.
See also: The Notebook.
The Real Ending: Three months later you see him dancing in a club with some chick in a tube top.
The When Harry Met Sally Trap: You've never been attracted to your male best friend, but recently things in the romance department have been less than enthralling. So you start to wonder; maybe, just maybe, The One has been staring you in the face all along.
Who cares if he still lives in his mom's basement? This is destiny, damn it.
The Real Ending: Prepare for an awkward, tequila-induced make-out session that definitely requires an "I don't know what I was thinking" email the next day.
The Titanic Trap: You just made partner and need to focus on work, but you can't get this new guy off your mind. His name is Bo, he never went to college, and he works at the burrito place where you sometimes grab lunch between clients.
Your friends ask what exactly you hope to gain from this relationship, but luckily you're not a snob like them, and you know that a person's job isn't what defines him.
See also: Sabrina, Pretty Woman, Sweet Home Alabama.
The Real Ending: At a company dinner, your boss asks Bo what he does and he replies, "I work the grill, but I'm hoping to be put on the register soon." Face it: If Leo had made it to dry land, that relationship would never have survived.
The Stepmom Trap: None of your romantic fantasies ended with Prince Charming leaving you for his secretary. Nor did they include falling for an otherwise great man with two sizable and unavoidable flaws (i.e., his children).
Don't panic. Contrary to what you might think, this divorce stuff is a piece of cake. Your stepkids hate you? All it's going to take to turn that around are some good old-fashioned sex tips from you (to make the brats more popular, duh) and the untimely death of their mother.
Your ex couldn't seem to tie his own shoelaces when you were together? Rest assured that once you've signed the divorce papers, he will clean up his act and become the kind of guy you meant to marry.