[Frowning, Zero isn't one to spill the secrets of someone else, he has so many of his own he's trying to protect that he couldn't do that to anyone else.
But this is different. Yuuki is aware, at least a little, that Zero has been watching over Saya carefully. That he's been trying to protect her in his own way during their time here. She helped him contain her within the gym recently when she feared her control.]
She's afraid she's going to lose control again and destroy everyone. [Tongue tied and unsure how to explain things in a manner that would catch Yuuki up quickly, without having to force Saya to rehash everything for a second time.] It's happened to her before.
[Attention on Yuuki, he knows pushes forward adding another bit of information she'd want.]
Forming attachments only to lose everyone you care about over and over...because there is no one able to stay by your side. In her world, there was only the two of them.