[Don't go getting ideas into your head, Piter. It's less specific desire for you and more a general love of all things relating to sex - along with a fascination with the unusual and the dangerous. Piter qualifies as both, and Jack just wants to get closer, to experiment, to see what makes him tick.
He's not quite expecting the nails digging into his skin, and the sensation makes him gasp, fire flashing into his eyes for a moment. Then he attacks Piter's mouth with even more fervour, one hand sliding round to get a good grip on his hair. Piter deserves a bit of sting from his hair being pulled to counter the sting in the back of Jack's neck.]