I know that for some people this a real big issue being molested by family members and its a lot more common than most people think.I would bet that everyone of us has a relative that has been molested.Lots of bad things happen to kids this is just one of them.
But I would make sure this is your one big relationship. Sometimes men can get overly emotional about this issue at first and over respond in a bad way.If your going to tell him make sure you are in a secure enviorment where you won't be interrupted and you will have the time to talk the whole thing out.