Dean-
Ma and My Broke Heart by Rixton
He picked this song personally. He knows he's a broken man, but getting a little lovin' from you tonight makes everything seem perfect to him.
Sam-
A Sky Full of Stars by Coldplay
To him, your the stars to his sky. And just as the song goes, he'll give his heart an dlet you tear him apart.
Cas-
Stay With Me by Sam Smith
He heard you singing this song before and said that he wants you to stay with him, forever. He didn't propose though, sadly, but he gave you a necklace with a small silver heart on it.