I think you should keep your secret to yourself. If he's old fashioned, you probably can't change him, and you may wreck your relationship if you confess. Consider an alternative possibility: He likes boys and wants to bring one home to play your bed. How would you feel about that? Rejected maybe?
Have you ever seen the movie "The Sex Monster"? It's a sexy comedy about a situation similar to what you describe, but the story takes an unexpected turn when there's more than one woman in bed with a man.
I think you should keep it to your self. And keep having fun. I also like girls but i dont have the guts to play around. I wish i did, I no I would be happier.So for all us gutless bi`s, keep up the good work.