It's all bullshit, really. Beth's continued existence is a happy accident, something he doesn't deserve and revels in anyway. The real reason, because the Cetagandans wanted to use him as a weapon, because he stabbed one of their grunts rather than bow his head, because of the drugs they pumped into his veins... that's his business.

Spilling about how he knows Beth is a sacrifice, but a small one compared to the information he'd rather keep back.

"Beth," he says, "Beth Greene."