Daisy was driving when Myrtle was killed. She killed Myrtle but Gatsby is willing to take the blame and the consequences in order to protect Daisy. Daisy only wants to save her own skin. She is selfish and self-centered and Tom is only concerned with maintaining his status in the elite world of the rich and wants nothing to do with scandal. The external conflict would be the law. Daisy will not confess to the hit and run she committed and Tom would not give up his standing in the community to do the honest thing and go to the police with the truth. Daisy and Tom are content with allowing Gatsby to take the blame since it is presumed by some, namely Myrtle's husband, that Gatsby was driving the car at the time of Myrtle's death. Unfortunately for Gatsby, Myrtle's husband arrived before the police and killed him. Both Daisy and Tom are without conscience or a moral compass. They get out of town and never even attend Gatsby's funeral. Kind of hard to face a corpse when you are the reason they are dead.
The real meaning of euphemism friendly fire is term in military bases means accidentally attacking your own military unit hope this helps :)
