Personally, I've told my husband about every skeleton I can recall, normally not long after a similar subject was mentioned. He is also someone who believes the past helped make us who we are, but we are not our past. He has been amazingly understanding and supportive (as a really good addict and alcoholic, I have a LOT of old skeletons!) True love is understanding and compassionate.
Do you want to carry such a secret from your chosen partner? Maybe you might like to ask yourself if you would love him less if he told you some painful secret from his past? Would you rather he tell you in a calm peaceful time, or would you rather it come out at a much later date and feel like he'd purposely hidden it from you for years? You are who you are today because of every decision you have ever made. If he loves you for being you, then whatever you did before you got together should not change his feelings for you.
BTW, if you decide to have a child together, the doctor will ask if you're ever been pregnant and if it was to term or terminated early because it can sometimes have an effect on future pregnancies.