"You can make an opportunity attack when a hostile creature that YOU CAN SEE moves out of your reach."
In 5E do you have to specify which way your character is facing at all times? If an enemy who is behind him leaves melee range but his back is to him does that enemy provoke an opportunity attack?
Are enemies within five feet and 360 degrees of a character considered to be within reach?
For example... Kruska and Atone are attacking Dip. Dip is facing or only attacking Kruska.
Then Atone moves out of Dip's reach (melee range 5 feet) to engage a silly looking wizard.
Does Atone's move provoke an opportunity attack from Dip even though he's not facing him? Is he assumed to be able to see him?