Am I BI??!! Any advice would be helpful!?

Im 16, my life is football. Ive had a few girlfriends and usually find myself ending up with a girl at a party.I dont mind joking about with mates and stuff but nothing like this has ever happened. One of my mates stayed around last week and i dont even know how but we were like at it for about 20 minutes straight, this happened after watching 3 messed up films (the crazies,paranormal activity 2& and the human centapide dunno how to spell that;) ) but yeah, thing is ive ust come out of a relationship and i think i actually like a girl right now. But when i was with him i really didnt care i actually kind of liked it! We're close mates and we've talked about it said its alright just forget it, but the last time i went around the same thing happened, it just happens:/ and now i actually think i might like him. But i also like the girl ive been talking to for agesss and dont want to lose her:S im so confused.