I'm afraid the others are all right. I know you want someone to give some great explanation, but the fact is once you have sex you change the course of a relationship. If you back off it now, you will hit his ego, no matter how you explain it and even if he says he is ok with that. If you don't tell him and keep having sex, then you'll be unhappy and begin to have negative feelings towards him. I think the first option is your best bet but overtime that could easily ruin your relationship as he will wonder what is up with you, no matter how well you explain it. So be honest and tell him. Don't use the word mistake--he'll think you made a mistake about having sex with him. Just say you love him, want to be with him, but don't think you feel ready on a personal level to continue having sex, at least for now because you are worried about the potential risks/consequences of it.
