How to convince my friend suicide is not a viable alternative?

STOP!!!! Do not try this at home! This is for a well trained psychiatrist to handle. You call. You make the app't. You take your friend (because you are a true friend) to the first several app'ts; do ask the doctor to tell you when to stop accompanying your friend. When? Tomorrow!
Minor? Suicidal thoughts should not be kept a secret. Are you minors? If so, please let your friend's parents or guardian know. If you are comfortable with this, then tell your parents so that they can intervene. You can tell a school counselor. Even if you talked your friend into not committing suicide, the thoughts may return. Your friend needs professional help as soon as possible. Cudoos for caring!