I am a bachor. This question was posed to Rabbi Twerski and he said that he felt you must share it with her after you are serious (links below). A while back I was dating someone a number of times and, with MUCH hesitation I told her. She was shocked and appalled. I asked that she talk to a Rav about it, which she did and she continued to date me.
(There was no happy ending I broke up with her myself at a later point)
This is a very hard one. I told claim to have the answers. I am sharing what I once did. I do not know how I had the courage to do that and do not know I could do it again.
I will pose a question to you:
What if she catches you after two weeks of marriage? what will that do to her system? What about after ten years and she realizes it has been going on for years?
here are some links on the site about this:
Do I have to tell my date about my "past" addiction?
www.guardureyes.com/GUE/RTwerski/Dating.asp
When Can I Start Dating?
www.guardureyes.com/GUE/RTwerski/startDating.asp
Dating as an Addict
guardyoureyes.com/articles/rabbi-twerski/item/dating-as-an-adict
Dating Experience
guardyoureyes.com/articles/testimonials/item/dating-experience