He'd been kept in the dark, hadn't realized how weak it had made her. He would have stopped her otherwise, demanded she let Osiris kill him, or one of the Eyes. He felt responsible, so he'd deal with this.
Even if it made things worse. Even if his temperamental actions wouldn't get him the sweet embrace he'd been missing. It was perfectly worth it if he'd see, with his own eyes, that she was well. He'd even badger her priestesses to pray more, harder. He'd go through a lot to get her on her feet. Only then would he leave, and as quickly as he'd came, as she'd told him to.
He opened his eyes, "I'm very well aware of what, and why, you did it. You should have told me, and I would have gone to our brother. I hear he's very anxious to repay my past deeds. He would have done it with glee. You still did what you wanted, and I didn't see the aftereffects and was unaware. We're both very stubborn Gods Nephthys. You got it in your mind you'd kill the demon, consequences be damned. Well now I'm here to make sure you'll be alright, consequences be damned." He smiled at her.
"Just as you drew the blade through my neck, I'm right here without any intention of going anywhere. Once you got your color back, your free to kick me out and I won't say a peep. And Princess," it wasn't something he used often that title of hers, "we both know I'm far more stubborn then you. Besides, like it or not you can use my help. You keep forgetting how alike we are and how you can use some of my power to strengthen yours."