I'm looking for a [spoiler]

(manga
/manwa or webtoon, can't remember which), about a girl who poseses a concubine from a tribe that married her off to a emperor, but then she ends up having an affair with the emperors right hand man instead.

I remember that there was a what or silver haired guy who was the original body's lover but he betrayed her. The emperor allowed the affair but by law had to send the girl to a island to be by herself at the end of the novel.

The ML had long hair and glasses, and was a war tactician.

Thanks for the help I am tired of endlessly looking through romance, isekai, historical tage

Kinda sounds
Yume no Shizuku, Ougon no Torikago
But the guy didn't have glasses... or long hair lolol

Maybe this one?
Revenge of a Fierce Princess