well, this form of relationship can happened in real life (even if in this manga is over the top). But yeah, Ruka it's so desesperate that she sell out her first kiss as a last trump card (I feel bad for her). And the mc, after all the precedent events, he can't even tell what's going on with Ruka behaviour before the kiss ? I know is for the sake of "drama" but there is a limit to be so clueless. The author need to wrap Ruka history to give the mc some developement. And give Ruka some peace of mind by dropping the mc. She is wasted on him.