Forgotten Title engagement breaking, prince want step sis, can't bc step sis not adopted in marquis family

engagement breaking, prince wants to get with her step sis. can't, cuz she's not a marquis daughter despite being step sis bc she wasn't adopted into the family when marquis remarried. Doted on by father

 

This is prob not it,, but have similiar vibes
'nightmare graduation party' manga anthology chapter:
https://mangadex.org/chapter/1231547/2

I will still look 4 your title trough!!

 

It seems to meet every requirement, right down to the doting father. Though "prince" wants step-sister instead does seem to be way to common a trope
.
Incidentally, that is the only one from the last volume of that series I managed to read through to the end. (finished every story in the previous volumes)

 

Lol
I also couldn't read last volume, exept for 4th and 5th (this one) chapters x'D

Ps. @driedsaku , i couldn't find it

 

Wait,, maybe it's this: https://www.novelupdates.com/series/konyaku-haki-suru-kawari-ni-ka-to-wa-en-o-kira-sete-itadakimasu/
This title has some differencies from ur explanation, but still kinda similiar

 

Btw who does father dote on??
MC or step sis?

 

father dotes on mc