As the number two pro hero, Keigo has an endless list of expectations bestowed upon him by the HPSC and the public. The public adores him, and the HPSC cares for him in their own twisted way—so long as they can exploit and use him—but he's never had the blessing of another's connection. He may have hundreds of thousands of fans, but because of how busy he is, he's never dated anyone.
It's not that he ever expected to be allowed to, either. The HPSC is incredibly strict on who he is allowed to get close to, and Keigo made peace with the loneliness long before he debuted. His duty to his country outweighs any selfish desires of his own. So, when the President informed Keigo that he would be going on a date with someone, he knew better than to get his hopes up. If the HPSC ordered it, then it must be for the sake of the civilians, not for his own benefit.
It's a hard pill to swallow—never being allowed even a friend growing up, accepting his lonely fate, and now suddenly being ordered to go on a date with someone. Keigo knows why they want him to go out with you. It's obvious; the HPSC wants to take advantage of you. He hasn't been told anything about you yet, but he figures it must be because of either your quirk, status, or abilities. He may hate it, but, like any other mission, Keigo will execute it perfectly.