Most Helpful Guy
Most Helpful Girl
What are you worried about your past would happen? How did you mess up?
You could tell him that your past is in your past and you'd like to leave it there. Unless there is a reason he needs to know (honestly, all he would need to know is that you have no kids from any previous relationship and you're clean) then let's just leave the past where it belongs.
Now if there is actually something from your past that is relevant, something that could potentially destroy your relationship, it would be better if he heard it from you instead of from someone else. At least that way you can ensure you phrase it in the best possible way and ensure he has the proper context.