"You might not want it now but honestly, that doesn't mean you'll never want it," Zacharias said in expasperation. "I can honestly tell you that at this moment, I have no desire to shag you." Not someone who was indiorectly accusing him of doing horrible things in the future!
But he had snogged Merlin, and had wanted to snog him again. He was pragmatic enough to know opinions could change.
And then he saw the expression on Merlin's face. "Oh bloody hell," he sighed, some of his anger deflating. "Don't... don't go getting all sad. You don't even like me, so it's not as though you've anything to be sad about."