Moral values aside, depends on the situation. Let's say it's just plain killing your friend, wouldn't that mean that you would be considered a murderer for doing so? Hence the pointlessness of killing your friend, your life is practically useless unless you're willing to live out the rest of your life as a murderer. Considering the person is that big of a dick to make you choose, I doubt he wouldn't let you go or let you go free without any kind of information slipping to the authorities. Regardless of the situation, I will make it my objective to kill that person, should I kill my friend and get revenge.