"Evermore Without You" - Woman in White
(*Spoiler* doesnt matter anymore though

: Walter is mourning the loss of his love Laura, whom he believes dead)
"When I Look At You" - The Scarlet Pimpernel
(Don't know if it totally applies, but Marguerite is singing in reference that she no longer "knows" whom she marries, as she thinks he is a totally different person)
"Where's the Girl?" - The Scarlet Pimpernel
(Chauvelin tries to "seduce" Marguerite back to her old "affair"/love she had with him. But Marguerite is married (see above :)) and does not return the love for Chauvelin)
"Someone Like You" - Jekyll & HYDE
(Lucy is singing of an unrequitted love for Dr. Jekyll, not sure if this one would apply either!)
Hope these helped!