Well given that the Game/Opening explorer are fair game during correspondence games, I don't think it is terribly illegal. You're merely asking another human being rather than a chess.com tool. Though it does beg the question => Why would you want to know something prior to the game actually finishing? Your opponent evidently didn't want to play against a team ... he agreed to just play you.
Rule Question
Sort:
I know it's forbidden to post a position from an ongoing game. That makes sense. But while this may be obvious to some, I'm not sure if it's also against the rules to ask an opening theory question related to an ongoing game. Can anyone fill me in on this?