Sam accidentally gets married to a certain Slayer while in Vegas, and learns to make the most of it.
THREADS:
it's a long shot but I say why not (in which there is yet another accidental marriage)
on the other side of a street I knew, stood a girl that looked like you (in which Wolfram & Hart gets to an amnesiac Buffy and gets her to go after Sam)
and she picks up all the scattered pieces of her life (in which there is a reunion)