A girl (black hair) is reincarnated and becomes the empress instead of her sister. The emperor however pays her no attention and has a lover (red hair). I forgot what it was called
I found it! It's "lady to queen"
https://www.mangago.zone/read-manga/lady_to_queen/
Manga/manhwa with unrequited love and heartache? Isekai, yaoi doesn't matter which genre
I don't know if you'll like it but here:
https://www.mangago.zone/read-manga/twelve_nights/
The romance part is kinda complicated... What I mean is A is in love with B but B is in love with C but C is in love with A.
- https://www.mangago.zone/read-manga/first_bite/ (sequel: http://www.mangago.zone/read-manga/renchin/)
- https://www.mangago.zone/read-manga/seto_no_omise_no_okyakusama/
- https://www.mangago.zone/read-manga/kakugo_wo_kimete/
Thanks, I'll check it out!
I already read this, but thank you :)