How do I know if I'm bisexual?

I have to admit I am very confused about my sexuality. I usually hang around guys, I am a feminine looking girl but I do like sports. Point is I do seem to be attracted to some girls, for example if their wearing a tank top and it shows cleavage or if they have nice *** I'll notice and might even glance. No I have never kissed or done anything with a girl, however I do find myself sometimes wanting a kiss, I am very picky about girls so I tend to joke around with my friends when they or I point out a cute girl but there starting to think I like girls even though I have a boyfriend. don't know, am I bi? How can I find out?