What do you call this?

Maybe infatuation

I think, you can call it the same what makes the music appeal to Jean and drives him to listen to it (again): beauty, rapture, and so on.
The same motive, people want to find out, which song was played in a certain moment in a movie, like here:
http://www.imdb.com/title/tt1285246/board/nest/174638955

Moreover Véronique is an educated (contrast that to his wife in the opening scene) and a classy (think of what you associate with classical music) woman. Certainly she fascinates him, a simple man, and arouses his desire.

Edit: Also read this post: http://www.imdb.com/title/tt1285246/board/inline/177736422?d=177736422 &p=1#177736422

They didn't even kiss on the lips until near the end of the movie. Although they did consummate the relationship eventually, I think it was far more of a romantic love type match than one based on lust.