
The seme doesn't seem to love the uke, at least not as much as the uke does to him. Also it seems to be hes the type that gets bored easily and gonna need constant exictement and new things in life, so yeah sooner or later its gonna happen again. This story had pretty realistic /hateful seme but the ending could have been bitter.

What the guy said in chapter 15. But aint' our MC a princess as well?

She's actually not..
I mean no royal blood at all. Since her mother is not consider royal blood and her father is a commoner. The case of her little brother is different since his biological father is royalty..
Most likely our mc is a commoner they just treated her a princess in name because that what her little brother want.
B/c these two people seem like they are just right for each other. This doesn't justify all the nonconsensual things but I think some people could do much worse in the name of love. At least the seme has the right mind to know it was wrong. They are both decent characters I suppose.