The past is. The choice is whether your precious energy is spent on running from it or building the present using it solely as a reference. Even then, the past results of actions and behaviours were likened to the identity and energy of a you long gone. There is chance in every individual within each moment, and such that person is less than a shadow of the present you. With this stay reminded that running from our past leads right back around to it. That those you have left behind or have left you behind have done so for the greater good of all, that God or the universe or what have you, makes zero errors. Holding onto the past in a desperate tangle to re-live even a second of it, will lead to the collapse of the gratitude and appreciation of the present. This life is shorter than many realise, and it is even further shortened by spending it all wishing away for the past. Those moments would have been sobered and destroyed had you sat as you do now in those older contexts. We make the memories to the moments we cherish through being present in the moment here and now. Appreciate that instead.
Meditate.