What are some sad songs about loving someone who loves someone else?

Well... in the past few months I fell for a guy I probably shouldn't
have. He loves someone else though, and I am happy for the both of
them. It hurts to know he doesn't love me back... my heart is
obviously torn in two right now, but I think it's for the best that he
is happy and with someone else. Anyways, any songs for this,
preferably sad ones? ): Ones I can relate to at least. Thanks. :)