He tells Caleb that Ava is merely using him to escape the compound, and reveals his real motive for inviting him: to see if Ava can be convincing enough to trick a human into helping her escape.
He tells Caleb that Ava does not love him but is merely using him to escape from the compound. Nathan divulges his real motive for inviting Caleb: to see if Ava can be convincing enough to trick a human into helping her escape.