Your friend is suffering from a debilitating disease that has put her in constant pain and agony. Finally, one day, she decides that she really wants to die. However, her condition is such that she cannot die on her own. She is begging and pleading with you to help commit suicide. This would, of course, beillegal. What would you do?
Whatever happens, us humans are forbidden to kill because God is the only one who gives life, therefore He is the only who can take it away too. And besides, if he/she really is your friend, they won't ask you to be their murderer.
