After everything they've been through, the first thing Charles doesn't seem to detect from Erik is the one thing he didn't expect: affection.
Affection as a friend? He hoped. Charles F. Xavier would admit that any day, that he valued Erik Lehnsherr as a friend, and certainly a close one. But there was a single moment, in the midst of chess, that a single emotion that threw Charles completely off guard seemed to appear in the middle of nowhere.
Now, Charles wasn't cheating - of course not. It wasn't nearly as much fun that way. No, he was just keen to emotions at this moment, blocking off physical thoughts and strategy. He couldn't block Erik out completely, however. Whereas the typical girl at the bar (inebriated or otherwise) was easy to block out entirely, Erik was something else. He was a force, a magnetic one (no pun intended), that pulled Charles' thoughts towards his.
So when he sensed a different emotion in the split second of a move that seemed pointless, Erik paying attention to the chessboard with a half-smile on his face, Charles paid no mind to it. He knew Erik trusted him. And, well, he could be wrong. After all, he had said himself that humans were so much more complicated than simply what he sensed. It could just be a higher level of friendship, teetering on a line between companions and true friendship (what Raven would call being a 'best' friend), and not in any... romantic connotation.
That was just it, though; Charles wasn't sure. It must have reflected on his face, because in the next moment Erik gave him a look as he moved his bishop. "What's wrong, Charles?"
The other man simply smiled, moving his knight. "Nothing, friend. You simply surprised me with that move. I'll admit I expected something different." For now, then, he would simply assume friendliness. That was all it could be, right? Erik, Charles had assumed long ago, was not interested in men, especially not the likes of him (not that he wouldn't mind, but he'd never say that out loud). That was all it should be.
"Whatever you say, although I'd say you look a tad bit flustered myself."
"Is that so? Well, I was thinking of a pretty blonde I met at the bar sometime ago. Gorgeous, with the most stunning eyes - blue and green. Doesn't she sound stunning?"
Charles tried to ignore the disappointment that came like pulse from Erik's strong control over his emotions. The other man seemed not to notice his slip. "That she does. Ah, check," he said, and they continued with their game. Charles stifled his suspicions.
But after that, every brush of skin, sideways glance, halfway smile from Erik seemed powered by something far more intense than that glimmer that Charles had felt that day.