...If you tell anyone about this I will gut you. [It's pretty clear that he could do that.]

I've told you before that I'm not the most moral or sane person in the world, before I met Gon I'd gladly see the world burn if it was interesting. Now I would happily burn the world myself it it made Gon or my little sister happy. They are the most precious people in my life. While Alluka already knows my feelings about it. I love my little sister...and it feels the same but different with Gon.

...I don't think I've ever said it that to him.