Brian in Love is episode 04 of family guy season 02. It was originally aired on March 7, 2000.

When mysterious stains appear on the Griffins’ carpet, they assume it’s Stewie.  But when Brian finally confesses that he made the mess, Lois encourages him to seek therapy.  In an attempt to end his uncontrollable problem, Brian tours the world in search of himself.  But nothing prepares him for what he discovers: he’s in love with his best friend’s wife.