Hearing Theodore's words, Aileen could only nod weakly, showing her feminine side that needed protection from this man, something Theodore liked the most and Aileen understood very well.
As a man, Theodore needed this kind of security; a feeling of being able to protect his woman, a feeling he didn't get from Hailee because she was too independent and rarely showed a weak attitude like Aileen did whenever they were together.
Theodore felt in control whenever he was with Aileen and he loved her.
Because of that, he didn't really have any deep feelings for Hailee, as he didn't really like her character who was difficult to control.
But without Aileen knowing, after meeting Hailee again earlier, Theodore felt something different about her and he couldn't say what it was... it was just that he was used to see that girl as someone belonged to him and now when Hailee was with another man he felt like something was taken away from him.