I am surely not a music expert at all but this song is mesmerizingly romantic: Stillness of the Mind by Abel Korzeniowski (soundtrack of A Single Man).
It’s not exactly classical but a refreshing take on modern classical composition. The space and tension explore a palette of emotions, from melancholy, to sadness, to utter despair adding touching aspects to the film’s beauty and dance through it gracefully. If you haven’t watch the movie, watch it, seriously! however, even stand alone as a song, it’s beautifully heartbreaking.