Hmm its a tough one but I think you jsut have to be honest with them before things get too serious, probably before you sleep with them. I got a pretty healthy habit for something a while back but I think it is all about how you portray it. If you are shy and try to hide it, they may think you are sneaky and trying to hide an active addiction but if you are upfront about it and explain why (major kudos for vulnerability and openness) you should do alright.
So anyways don't ever try to hide it if anything say something like " I made a lot of mistakes in my life but every single decision good or bad has led me to this moment, with you. So in a messed up way its a good thing and I learnt so much from that experience etc etc"
Hope that helps
