Looking for a song...?

I'm looking for a good song to represent the longing and pining over a past first, and unrequited love. Knowing it's only really a memory of a more carefree time. I've moved on long ago and am happily married with 2 wonderful children, but it's hard not to remember the past with intense fondness. Feeling nostalgic and looking for a song to represent... Thanks for any tips in advance!