Is it normal my thoughts are changing

I have a problem , me and my best friend always mess a round ' like 'well your looking sexy , id tap you into a coma and back' but lately we both say it a bit more truthfully , were both girls and ive known her all my life , a lot of the time i think about her sexually , shes emo /scene and alot of those girls do 'experiment' im not emo but i really wanna take things further , any tips? Any will be accepted thanks:).xx
p.s ive always been straight and so has she but i think thatss changing... Xxi want to know if its normal that i suddenly want to be sexual with her by the way