Entity Listener - Before Delete

Hi guys,

I have an entity that I don’t want to be able to delete if there are similar entities with a date after the one I am trying to delete.

entity 20/01/2017
entity 21/01/2017 <---------
entity 22/01/2017
entity 23/01/2017

If I try and delete the entity for the 21/01/2017 I want it to not delete it and show a notification explaining why.

How would I go about this in the listener? Is it possible? I cannot see any methods to override…