Personally have nothing against any sexual preference. Straight / bi or gay. If it's consensual and not forbidden by the countries laws - embrace it and go for it if it feels good to you. Who cares what anybody thinks. If the activities happen in the privacy of your home or an environment when such is encouraged - its nobodies business anyways.
Mrs2 expressed her fantasies of seeing me engaging (not penetrative - just manual and oral) with a guy. So we have explored. Turns out the fantasy was better in her imagination than how it played out before her. So we don't explore it any longer.
But... I am inclined to agree with Haveusbc. If you find yourself fantasising about a bi experience with another male; by strict sociative definitions, you are not 100% straight. Perhaps mildly bi-comfortable is a better term of reference?