Erm, that stuff's illegal, and no, it's not your fault whatsoever. If a child came and talked to you about the work you were doing, would you see it as a sign that molesting them was ok? I think not. I don't really know what to suggest, but telling your parents that this friend of theirs molested you might be a start - but obviously I don't know the situation, you've got to decide whether you think that they're the right people to tell. Remember that he may have done/be doing this to other children as well; you may not be the only one.