@ah0_13aka
This is a very old one (published 1995) and unfortunately is on Hiatus, but it's my first romance manhwa with Western setting. There's a lot of drama and heartbreaks if I remember correctly.
https://mangadex.org/title/8367/princess
Tale of Felluah comes to mind-- not sure if on mangadex, or if it is still getting translated, but this is some good medieval-based manhwa
Also worth mentioning:
Usotoki Rhetoric - not set in castle but is western based (?), has a really good side of romance
Colette wa Shinu Koto ni Shita - not so much western hahaahahah but still good