The relationship between the billionaire Microsoft co-founder, 65, and his philanthropist wife, 56, had long been splintering before it came to its end, a source tells PEOPLE in this week's issue.
"He could have treated Melinda better," the source says. "He's not a saint, but there isn't one thing that created the final split. It goes deeper than that."
"It's many years of differing views of the world, the foundation, and of life in general, and those things piling up. They are older and each personally looked at life and asked, 'Is there more out there than what I have?'" the source continues.
The couple share three children (daughters Jennifer, 25, and Phoebe, 18, and son Rory, 21), as well as the Bill and Melinda Gates Foundation, which they have said they plan to continue working on together.
Daniel Berman/Redux Bill and Melinda Gates
Despite their united front, the source says that the pair's statement, in which they said they "no longer believe we can grow together as a couple," rings true.
"They've grown apart for a variety of reasons," the source says. "She's more interested in women's issues and what and who they helped with the foundation. Bill was — and is — far more interested in the business side of his life."
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Melinda has in recent years focused her efforts on causes near and dear to her heart, and in 2015 launched Pivotal Ventures, an investment and incubation company geared toward helping women and families.
She wrote in her 2019 book The Moment of Lift that she'd struggled to find her voice in the many years she spent speaking beside Bill.
"He needed a better balance. He needed to let her speak and take the recognition she deserved on many foundation issues," the source says. "He didn't realize he made those mistakes when he was making them."
In addition to the power dynamic, there was also the lingering issue of Bill's ex Ann Winblad, a prominent venture capitalist with whom Bill reportedly took a Melinda-approved long weekend each year.
While the source says Bill's friendship with Winblad outlasted their breakup due to their many mutual interests, her presence may have contributed to a deterioration of trust.
"He is close to her. Romance or not, when one spouse loves the company of another person outside of the marriage and perpetuates that friendship over many years, it can help destroy trust," the source says.
Though Melinda reportedly began seeing divorce attorneys in 2019, she officially filed for divorce last week in documents that said she was not requesting spousal support or child support.
The only thing Melinda's documents asked for was that the court enforce the couple's separation contract, which is an agreement to resolve issues that would otherwise be left to the court to determine, like division of property, support and child-related issues.
Reporting by LINDA MARX