Bruce Springsteen's "Glory Days"
Bryan Adams' "Summer of '69"
And there appear to be songs called "Where have all the good times gone" by Elton John, Van Halen, The Kinks, and David Bowie, at least. Not sure how many of those are covers. [Edit: Also, noting that we're talking something less specific than a relationship, like a whole era.] So, as a reminder not to be self-defeating, give me some others if you can think of any.