Jennifer Lopez may have spent $20 million of her own money financing The Greatest Love Story Never Told, a documentary about her and Ben Affleck’s 20-year journey back to each other, but the film might end up costing her much more than that. A source exclusively tells Life & Style that while the actor, 51, will publicly support his wife’s passion project, privately he doesn’t understand why the singer, 54, wants to put their personal life in the spotlight. “Ben has gotten very good at biting his tongue, but it’s known that he’s not happy at all about J. Lo’s endless need for attention,” says the source. The Oscar winner confesses as much in the doc. “Things that are private I always felt are sacred and special because, in part, they’re private,” Ben notes. “So this was something of an adjustment for me.” In the film, J. Lo even allows a group of songwriters to use love letters that Ben sent her, titled “The Greatest Love Story Never Told,” as inspiration for her new album, This Is Me…Now. “Ben loves J. Lo dearly, and he knew what he was getting into, to an extent,” the source admits. “But his fear is that by putting so much of herself out there, J. Lo’s just opening them up to way too much public scrutiny, and that hasn’t helped their relationship historically — far from it.”