How we cite our quotes:
[Charlie] spun around to look at me, and I could see in his face that he had no intention of letting me leave. I could think of only one way to escape, and it involved hurting him so much that I hated myself for even considering it. But I had not time, and I had to keep him safe. (19.31)
Bella is willing to sacrifice her father's trust in her in order to keep him safe.
[Edward to Bella:] "I know, Bella. Believe me, I know. It's like you've taken half my self away with you." (20.139)
Edward points out they are now connected, and how her sacrifice is also his.
[Bella to Alice:] "I can't win, Alice. You can't guard everyone I know forever. Don't you see what he's doing? He's not tracking me at all. He'll find someone, he'll hurt someone I love…Alice, I can't." (21.18)
Bella realizes she is going to have to make the ultimate sacrifice to save her family. If not now, then sometime down the road.