There are millions of guys out there. Your "best" friend needs to realize this before she loses you. My best friend and I made a pact back in middle school before we even started dating that once we made known our interest in a certain guy, he was off limits to the other. And once we did start dating, anyone we had gone out with - even on a single date - was off limits. It worked very well and she and I never had a problem following our agreement because we realized how special our relationship with each other was and how no person should (or would) ever come between us.