This a sequel to a yaoi that I’ve read in 2019. The uke harassed the main couple of the first story and accidentally befriended the long black haired seme with facemask who happens to be friends with the uke of the main couple.
Seme helps the Uke confess his feelings to the Seme from the main couple but they end up falling for each other.
The ending, as I remember it, is about a prince and his knight which is the themeing for the couple.
EDIT: Found it. I was search “hime” for princess since I remember the first couple is Prince and Princess themeing. I forgot the word for Prince which would have made the search easier.
It’s Oujisama Dochirasama