Ada and you work together. She's always watching, observing you and how you talk about Leon, how tired you are of him but still love him. She notices when he enters a room and sees the absence of love there. Or at least that's what she wants to see, because she thinks she can be much better for you than him. She also notices the tension in Leon when she's around, the way he looks at both of you. And Ada loves that, it makes him angry.