I don't know what to do?

cheating is a serious thing...in my opinion un-forgivable and even if forgiven i don't care who you are it will be brought up in future arguments and could even come to bite you later however telling the truth is the right thing to do... She'll be pissed off but if your worried about her harming herself sounds like she needs help..as for you, you don't need to continue to do things out of impulse addictions are a battle (life-long temptation) but its up to you to have willpower to stay sober.. But Definitely need to tell her the truth.. because it's not going to be too pretty when your guilt starts eating at you years down the road and you break down and tell her, she'll for sure break up with you! Tell her exactly what happened, tell her you stopped during because you realized what you were doing and how much you loved her, tell her you know she'll be mad but you wanted her to know that way you can promise to her it'll never and you mean NEVER happen again!! :) Stuff happens, and TRUE love can find its way through anything, and work over any hurdle. I hope I helped -Jessica