I Wouldn't Marry You - The Gay Life Men - Whoop-Up Quarrel-tet - Whoop-Up You Don't Know - Here's Love She Hadda Go Back - Here's Love What Did I Ever See in Him - Bye Bye Birdie Shall I Tell You What I Think of You? - The King and I
The Very Next Man, from Fiorello Forget about the Boy, from Thoroughly Modern Millie What Chance Have I with Love, from . . . a couple of different shows, I think!
"We Do Not Belong Together"- Sunday In the Park With George. Although there is obviously love between them, it's more heartbreaking, in my opinion, to love someone knowing that they could never love you back fully and then have to move on from that.
^In that vein, I think "You Don't Need to Love Me" from IF/THEN fits too. I didn't care about the character in the Beth timeline, but he was all sorts of pathetic unwanted puppy in that song.