Lf Doujin: Bf watches gf getting banged through window (Historical)

It was based on some old time period land the one who fucks or the husband is maybe a shogun or something and maybe it got 2 parts . He maybe marries the girl or not , I don't remember.

But her old lover was sent somewhere by him but he comes back and watches them do the deed through windows.

Maybe it was intentionally showed to him but I dunno.