His past?

I've been with my boyfriend for almost a year. He decided early in the beginning that we should be open and honest about our past sex lives. I was fine with that, being that I had only slept with one other guy. He told me he had been with 15 women, including myself. He has been a very honest person with me...until he came back later on telling me that the number was incorrect and that he had really only slept with 8 people in all. When I asked him why he would lie about that, he said he wanted to look more experienced. It has bothered me because I'm not sure what to believe exactly. Also, I've known many of the girls he has been linked to, one that I've known for years. The idea of him sleeping with her literally sickens me. I know I shouldn't care with that being in his past...but it does. I see her so often and I'm always with him. Am I wrong for being somewhat bothered and worried?