In a Betty and Veronica love triangle, the Betty somehow becomes the Veronica, and vice versa.
This can happen in two different ways:
The Reveal: The sweet, homely Betty is actually Cute and Psycho, and the haughty, fascinating Veronica is actually a Jerk with a Heart of Gold. Archie was a Horrible Judge of Character all along, and really should run before his "wholesome", "soft-headed" [...] [tvtropes.org]