Jennifer Lopez has spent $20 million of her own money to finance the documentary film “The Greatest Love Story Never Told,” about her 20-year journey with Ben Affleck, but the film could ultimately cost her much more.

Life & Style, citing a source, reports that while the 51-year-old actor publicly supports his wife’s project, privately he doesn’t understand her desire to put their personal life on display for all to see.

“Ben has learned very well to hold his tongue, but it’s known that he’s not thrilled about J.Lo’s endless need for attention,” the source says.

“Personal moments, which I’ve always considered sacred and special, partly because they’re personal,” Ben notes in the documentary film. “So, for me, it was a kind of adaptation.”

In the film, J.Lo even allows a group of songwriters to use love letters sent to her by Ben, titled “The Greatest Love Story Never Told,” as inspiration for her new album This Is Me…Now.

“Ben loves J.Lo very much and, to some extent, knew what he was getting into,” the source confesses. “But he fears that by exposing so much of themselves, J.Lo is simply opening them up to too much public scrutiny, and it hasn’t helped their relationship in the past.”