Greed.
Nino's words struck Sam at a very sensitive place. He felt exposed, and his chest was filled with a strong sense of disgust directed at none other than himself.
It was true that he did at one point consider the Valkyries as nothing more than playthings. Back then he was under the belief that they were nothing but robots, and ones created for the sexual pleasure of men at that. He didn't care about their feelings and just wanted to toy with them as he wished, but a lot of things have changed since then.
{... So you're jealous after all, huh, Nino?...}
"Eh?"
His desire to sleep with the Valkyries was still as strong as it was back when he couldn't even dream of laying a finger on them. Now that he was in a position to access each and every one of them, he planned on using that privilege to its limits.