How can I stop being attracted to guys?

This letter reads:

Dear Dr. Powell;

I am an 18-year old male. My problem is I think I am a queer! I love making out with girls but when I see playgirl books in a magazine store I have this urge to go and look at the men’s penis’s. And I get erections. Even when I was going to the high school in the shower rooms I always had a fantasy of “making it” with some of the guys that were “well hung”. How can I go about getting rid of this hang-up?

Name & Address Withheld