If he had arms, they would have been dramatically draped over his forehead at the mere thought of his broken heart. "betraying me." Tiny sigh. "'oh mettaton, i told you to be careful!! i told you not to get yourself hurt!! i'm out with my girlfriend, who i love more than you, so you're just going to have to rot there on your vacation with the moon of your life'," he helpfully paraphrased in the least flattering imitation of his best friend. It's awful when you can't mechanically adjust your vocal cords to be a perfect match, so nasally (?? he doesn't have a nose??) whining will have to do.

The question about said moon of his life causes the core to tense up a moment. There really isn't much reason why. Reflex, maybe. Holding secrets for so long tend to make you jumpy at the thought of spilling them, even after you already have. "...yes. he knows."

Well.

"ha... he actually already knew." And not because of Sans! Thankfully. Sans was a decent fellow; Mettaton would hate to kill him.