The Fionavar Tapestry trilogy, by Guy Gavriel Kay is one of my favourite. I simply love it. It takes place in another world, but there are knights and kings and princes and princesses, seers and myths, and Old Religions and New Religions, and King Arthur and Lancelot and Guinevere and The Wild Hunt. It’s dark and exciting and beautiful. 
All of his books are fantasy inspired by very specific historical periods. I think A Song for Arbonne, which I remember being good, was inspired by French Medieval times, but I’m not sure.

There’s romance in both of these, but not only. 

I can’t think of anything that would be more specifically romance and also fantasy that I have read. 
Maybe, The Lioness Quartet by Tamora Pierce?

Oh! The Princess Bride, by William Goldman.