Hi Sara,
He may not want to lose your attention.
Even though he told you that he wasn’t interested, he may still love the attention that he is used to getting from you and may not want to lose that.
By continuing to make lots of eye contact, flirt and show deep interest in your life, he is hoping to stay relevant in your life so that you don’t start losing feelings for him.
Though he may not want to be in a relationship with you, he still wants to experience the emotional satisfaction of being desired by you.