[Zero could say that he had forgotten Ai as well - all over again - but right now this isn't about him. It also briefly has him thinking back to when Yuuki actually forced him to forget about her. However such a thought doesn't have any place here. It was for entirely different reasons, anyway.]
That, too, wasn't anything you could have had control over.
[His words aren't chiding. ]
But, you're hurt. [So very much so.] Ai will forgive you. I promise. Because that's how she is— she's your precious daughter, and she loves you so much. Even I forgot her. [ (I forgot you.) ] Just as you do, I'm so sorry that I had.