It Follows
(2015)

Jay (Maika Monroe) is the unknowing recipient of a curse, given to her after having sex with Hugh (Jake Weary).  The curse is an entity that follows the cursed until they have sex with someone else.  If “IT” catches to the cursed before they pass on the curse, they are killed.  At that point, the curse reverts back to the person before.  Jay and her friends then plot to kill “IT” before it’s too late.  At that point, they plan to lure it into a swimming pool and then electrocuting the entity.  After the ensuing chaos, “IT” is shot in the head, supposedly killing the entity.

Later on, Jay has sex with her friend Paul.  In the final scene, they are walking hand-in-hand and a person is seen following behind them, suggesting that “IT” is still alive.

Thanks Emilio!