if you dont tell him nothing changes.it is a sad thing from your past that plays no real role in your relationship.he loves you for you no matter how you got there so i say don't tell him.i realize you want to be totally honest and open with him but are you also gonna talk about "that ex boyfriend that was your best lay ever"as i see it things like that should only be talked about if it is going to benefit someone.the only think that can come from telling him is change.