By Chloe Stewart & Caroline Gaspich In Jennifer Lopez’s new documentary, The Greatest Love Story Never Told, Ben Affleck revealed the hilarious nickname J. Lo’s friends gave him after the singer shared secret love letters he’s written to her over the years. In the new film, Jennifer shared that she had kept a memory book overflowing with romantic, handwritten love letters from her longtime lover Ben, whom she first dated back in the early noughties. Jennifer treasured the letters, showing them off to her employees and pals, so they could share the same vision she did for her new album. During …