This is a very fast one and no sarcastic comments, if so I'll just ignore you. Ok, let's say if you're in a new relation, which happens to be the second, and he/she ask you the question you're not comfortable with.
He/she asked you "Have you ever cheated on someone", and well let's say you did, would it be better to just say "No" and leave it that way or bring your past again. I say the first option is better, why bring the past, besides you're in a new relation, you don't want to already yet break another trust in that person by answering yes. Well just a thought.