It's almost impossible to imagine our grandparents when they were our age — let alone what they were like when they first fell in love. When photographer Lauren Fleishman found a box of love letters her grandfather wrote to her grandmother during World War II, they revealed more than just the fact that he was incredibly romantic."They were able to show me a side of my grandfather that I hadn't known: him as a young man, filled with the joy of being a newlywed," she explained to Refinery29 over email. "In one of the love letters, my grandfather wrote to my grandmother, 'I love you with all my heart, and will continue to do so for the rest of my life.' As a young woman, it was the type of sentiment I could understand and relate to."But the letters weren't just a meaningful piece of personal history. They also inspired Fleishman to launch a massive, six-year photo series devoted to documenting the love stories of long-married couples from all over the globe. A beautiful book version of the project came out earlier this year.As for whether anything she learned from these couples can apply to you? "Many of the couples were first loves — and they didn't have the experience of being heartbroken or picking up those pieces and trying again which can be really tough," Fleishman says. Still, there was one piece of repeated advice that stuck with her: "Relationships evolve over decades. Many of the couples said you can fall in love with the same person over and over again."Ahead, meet just a selection of couples from her incredible journey — you might just learn something about love in the process.