what would you do if were stabbed in back by a friend?

i think that i will confront my friend and ask him/her why he/she is stabbing me behind my back.. i would do so calmly because i may not be sure about it and i want to knwo his reasons. i dont want to lose friends so as much as possible i will keep them and forgive them. maybe they have done that because they have misunderstood my actions.. so i think that we should talk about it first and come up with an agreement. if he/she doesnt want to then prepare for the worst.. i am a nice friend but if you betray me and talk about me behind my bakc and hurt my reputation id do the same and more..

if he is a longstanding friend, i try to find out the reasons for his doing and sort out the matter. if he is not a close friend, i break up with him, and warn my other friends to be careful with him.