HELP! i have a problem! advice plz? :D?

ok well u see, i am a very nice person..a little too nice. like nice where u give some 1 something and i know they wont give anything back. er.. if a guy asks me out and i like him but once i get to know him more im not into him, and id rather him break up with me then me doing it, becasue i dont want to hurt anybody, or make them sad more less make them not like me. but..yah see dosent that make me a week person, to where i let people trample all over me? i am sensitive too. thats another problem. and being really shy. is it bad to lets say let some 1 ehh.. u dont like hurt you even tho it dosent hurt u 'bad' but still upsets u. ?