Help i need to know what to do...?

help - my husband and i had some fidelty issues - basically i thought he was cheating on me, i found some information that lead me to belive this. when i confronted him he denied everything - but i did not believe him as he did not look me once in the eyes to deny my allegations. neither did he chose to comfort me. we have a lovely young family and i did not feel he was being honest with me. however the problem is that same night i was discussing this with his best mate - we had a few drinks and i was feeling emotional - and a hug between his mate and i turned into a kiss - nothing more than a peck on the lips. we both realised it was very wrong and nothing more was spoken about it. i was stupid enough to tell my sister of this peck and she is now telling everyone i cheated on my husband and i am having a full blown affair with my hubby's mate. she has no proof and both of us know it went not further than the kiss. should i confess or continue to deny it happened at all? confused