Am I obligated to delete a Facebook account I created for my friend, which he is using poorly, knowing that this will affect our friendship, or should I leave it despite the pangs of conscience?

It is permissible to create an account for your friend unless you know or strongly believe that he will use it for something forbidden; because in that case, it is not permissible to assist him in that, due to the Almighty's saying: "And do not cooperate in sin and aggression" {Al-Ma'idah: 2}. And if you assist in disobedience to Allah, you are sinful, but if you are unaware of your friend's situation or the ruling, then there is no sin upon you. You are not obligated to take the account from him; rather, you should advise him not to use it for disobedience.