If anyone ever tells you that you put too much Parmesan cheese on your pasta, stop talking to them. You don't need that kind of negativity in your life.
The cult classic musical "Pokemon Live," notorious for its all-star cast and general weirdness, had the song "The Time Has Come," sung by Jersey Boys's Dominic Nolfi as Ash, as he loses his best friend.
It's actually a pretty nice song, especially for the strange show it's in.
"You travel alone because other people are only there to remind you how much that hook hurts that we all bit down on. Wait for that one day we can bite free and get back out there in space where we belong, sail back over water, over skies, into space, the hook finally out of our mouths and we wander back out there in space spawning to other planets never to return hurrah to earth and we'll look back and can't even see these lives here anymore. Only the taste of blood to remind us we ever existed. The earth is small. We're gone. We're dead. We're safe."
-John Guare, Landscape of the Body
Not classic showtunes as some have noted here, but "James" and "I've Loved These Days" from Movin Out fit the bill. "Fallen Angel" from Jersey Boys also fits... depending on what type of "losing" you are talking about.