I guess it depends for me.

Basically I feel like I am trapped in endless despair, and it is my greatest wish to get out of that (if you rephrase it, finding happiness might fit). If killing my best friend (which is probably one of the last things I would ever want to do) will allow me to attain that wish, then I will do it. The problem here is the content of the matter. What does ending despair/attaining happiness mean? Since that is unclear, or is not even feasible, then my final answer would be a No.

@Animeniax - wait, your greatest wish is to have 10 best friends? You clearly don't understand what the word "best" means. Besides, what's the point? In this case, quantity is not a factor anyway.