Would've been much better for me if there's a long and popular vn series like Muv-luv but medieval fantasy instead of mecha scifi. The only one i could think of was Kuroinu and that series is full of rape and gangbang shits.
"Long and popular series but based on medieval fantasy" is a rather broad category. Kuroinu and Muv Luv are nothing alike; Kuroinu is just a fap game if it fits your fetish while Muv Luv Alternative is one of the most praised visual novel of all time, to the point where the guy who wrote Attack on Titan said it played a large part in what inspired him to write Attack on Titan.
If you're looking for a story-based series that is medieval fantasy, then there are a bagillion of them since it's one of the most popular settings. Lord of the Rings, Final Fantasy, Harry Potter?, take your pick.
If you're specifically looking for visual novels than Utawarerumono is pretty popular by visual novel standards I think, although that is Japanese medieval fantasy rather than European. I'm sure there are others. I hear a few of the Rance games actually has a good story rather than just the usual wish-fulfillment BS.