How will you react if your best friend was not true to you

I never expect from my friends the thing i myself cant fulfill.... i always expect from my friend... upto the level i can do for him/her..... as far as the my best friend is concerned.... i never faced such situation so far.... and i believe in future too the same..... however... the supposed situaion mentioned in your thread.... will definitely embarras me however i will first dig out the reasons of that action of my friend.... without going through the facts behind the incidents i will never take any extreme step..