Should I tell her this dark secret, or not?

I have this friend who happens to be an attractive female. She ha a boyfriend. She comes over to my house quite a bit and she always turns me on. Like, something about her just triggers primal, animalistic urges within me! A few times, she has made me so horny that... while she was playing a video game... I wanked it. And I was in the same room, right next to her, with a blanket over me to cover it. I stared at her and pictured things and I'd *** so good. I feel guilty about it. But, I don't know if I should tell her. It has only happened a few times. What do I do?