“We can never go back,” bell hooks wrote in her moving reckoning with love . “We can go forward. We can find the love our hearts long for, but not until we let go grief about the love we lost long ago.” And yet we do go back, over and over. The tragic flaw of our species is the price we pay for the mind’s magnificent ability to move in time: the superpower of prospection that makes us capable of making a plan and making a promise comes bundled with the singular suffering of retrospection: the remorse, the regret, the past romanticized and voided of its own consequence. It is seductive, this selective time travel. The perfect weekend with the imperfect lover whose ineptitude at love you didn’t yet know would break your heart. The languid summer just before the diagnosis, the disaster, the death. The time you were ten pounds lighter and ten choices freer and ten mistakes less marred in the mirror of the mind.…