This is ridiculous!
1) You french kissed someone else only because he dared you (are you sure?)
2) You seem to be worried about what your boyfriend thinks and about how he will react although you went around leasing your tongue to someone else just for fun and on account of that you are not telling him.
3) You didn't tell him but, by now, there are at least a couple of million Yahoo users who know what you did, on top of the guy who (smartly) dared you, and whom can now happily make fun of you and your boyfriend.
4) Thanks for telling all Yahoo Answers around the world you have basically light-horned your boyfriend. He'll be happy to know you've been tasting someone Else's tongue for boredom and he'll be much happier to know he's been the last one to know (like an idiot), being left behind, even after all Yahoo readers.
Next question ( Paid with my points) will be: DO YOU HAVE ANY BRAIN LEFT???? Congrats!!