We've been friends for 16 yrs now. i dont know what to do anymore...?

we've been friends for 16 yrs now... but since she went abroad to study, i dont recognise her anymore. she's changed dramatically and has put me on a difficult spot more than once - in public. im usually a very hot tempered person but ive kept it on the low. i understand that we grow up, and things change.at some point she regarded me as ignorant and if & anything i said was replied by a 'u dont know, u havent been exposed to it' . she has undermined me once too many a times; she's kept things from me (now im at an age were i can accept things like that) now that she came back home she's in desparate search of me. i chose to let her be, as recently, after telling her something extremely personal - and emhasizing on the need to be kept between us- she went and ped on to a common friend which has a very hard time keeping things to herself as well. this has been the final straw for me, and an excuse to finally get the hint, and let her go. now she wants forgiveness.what should i do?