...I've killed. I've abandoned. I've allowed so many people to die. Adric- I... I waged war across an entire galaxy, left half of it in ruin before I was done, to bring down a single Time Lord. I watched my oldest, dearest friend burn to death, even as he begged me to save him. I...

I ran. I gave up on changing Gallifrey, and I fled it instead.

[He doesn't even know if he's saying this on his own or not, but he trusts her nonetheless, and would have told her willingly to begin with; it never occurs to him.]