It sounds to me more like your friend is a lesbian than you! There far too many factors to take into consideration to determine sexual orientation. You have not supplied information such as your age, have you had a boyfriend, do you prefer spending more time with girls or boys etc etc? The list is endless and you have not supplied enough information and even then one could not give a conclusive answer.
Lastly, there is nothing wrong with sexual experimentation with the same sex, in fact it is far safer than getting pregnant!
From that information, it is obvious you swing both ways and getting the best of both worlds. How lucky are you :-) I would just say go with the flow and eventually you will realise where to 'hang your hat.' If it ends up on two 'pegs' at the same time, so what! At your age it is easy to get confused about such things and a few years down the line you will probably be asking youself, 'what was all the fuss about?'
Enjoy your youth and stop worrying. Too much worry makes you age prematurely.
Sounds like your Bi if you must put a label on your sexual orientation?