The one wholly true thought one can hold about the past is that it is not here. To think about it at all is therefore to think about illusions.
You're always on your way somewhere. The key is: find a way to be happy wherever you now are on your way to where you really want to be. (We're speaking of the state of being you want.) It does not matter where you are; where you are is shifting constantly - but you must turn your attention to where you want to go. And that's the difference between making the best of something and making the worst of something.