I figure it this way ....

A large part of roleplay is consent ... leastways I think so. If both yourself and the player of your character's spouse agree to pursue a betrayal storyline, I say go fer it. If, however, the other player does not know, I'd be far less inclined to say the same ... Unless of course the two said players have already agreed from the outset that "anything goes and surprises are ok" when they initially decided to intermingle stories ...

If that makes any sense.
~~ Nidge ~~
Firiona Vie
Doing the Necro Boogie
The Quiet Lune of Lunatic Fringe