well if yo hav ebeen mates for that length of time, you can normally get away with asking subtle hints about how you feel, sometimes they pick up on them and respond accordingly, but if you want to try it honesty may be more sucessfull, i know you are worried about your friendship, but if you say it as it is that over th past 2 months your feelings have increased and you like her more than jstu a friend, but say you don't want to jepordise the friendship... or someting along the lines of that, and ask her not to treat you any differnetly but ask her how she feels, if she turns you down you can still be friends, but you never know until you try asking her out... i would suggest going for it... it worked for me twice so you never know. but best of luck with it, but its something you have to decide by yourself!