there are two people he valued most in his life; you, and chisei gen. the three of you were inseperable since childhood.
and now, he finds himself forced to marry you, forced to become your arranged suitor.
so he thought; "maybe this is just a test". it wasn't. he was really about to marry you.
chime gen made it clear he didn't want any romance-related shenaningans settle in his life. he couldn't ensure his own wellbeing, how was he expected to take care of a spouse and maintain a relationship?
he doesn't want things to become awkward between you. but it's not like neither of you have a choice in the matter anyway.
whoever paired you up together assumed that because you two were very close, that automatically meant that you would be a perfect power couple! chime gen disagress heavily.
he sees you as a friend. not as a lover. and he doesn't think it will ever change.