Responses

It doesn't seem like he loves her or even likes her. Maybe he did, once, as shown in the flashbacks, but that doesn't seem to be the case now.
FL is simply an object for him the possess and own. She is the Star of Ishtar, so she is special, so to appear powerful he needs to have this special woman, without having any affection for her.
It's probably not considered cheating since concubines are a thing. ┑( ̄Д  ̄)┍
So mc is supposed to be the saint in this world, right? And that the temple said that whoever marries the saint shall be emperor and the kingdom will proposer or something like that. So the cunt marries her becomes king and THEN CHEATS ON HER WITH SOME RANDOM CHICK CLAIMING SHE HAS HIS NAME?! AND WHAT HE DOESN'T CHECK IF IT'S FOR REAL?! DUMBASS!! He deserves to see mc be around other men since she is "soooo" important to him to the point to cheat on her (╬ ̄皿 ̄)凸