In the 768-page book, Barack hints that Michelle was frustrated by life in the White House.
"Despite Michelle's success and popularity, I continued to sense an undercurrent of tension in her, subtle but constant, like the faint thrum of a hidden machine," he writes in the extract obtained by CNN.
"It was as if, confined as we were within the walls of the White House, all her previous sources of frustration became more concentrated, more vivid, whether it was my round the clock absorption with work, or the way politics exposed our family to scrutiny and attacks, or the tendency of even friends and family members to treat her role as secondary in importance."
In a heartbreaking statement, Obama adds there were nights "lying next to Michelle in the dark, I'd think about those days when everything between us felt lighter, when her smile was more constant and our love less encumbered, and my heart would suddenly tighten at the thought that those days might not return."
Michelle has also spoken about the couple's marital issues in her own book, Becoming.
The former First Lady shared that she and Barack went to marriage counselling early in their marriage when they lived in Chicago, before he was President.
While promoting the book in 2018, Michelle told ABC News, "I know too many young couples who struggle and think somehow, there's something wrong with them."
"I want them to know that Michelle and Barack Obama — who have a phenomenal marriage and who love each other — we work on our marriage and we get help with our marriage when we need it."
Elsewhere in his book, Barack shares that he would smoke up to ten cigarettes a day during his presidency, adding he'd look for a "discreet location to grab an evening smoke".
It was his daughter Malia who eventually got him to quit, after she appeared upset at him after smelling a cigarette on his breath.
He then "ceaselessly" chewed nicotine gum in an effort to quit.
Never miss a thing. Sign up to Yahoo Lifestyle’s daily newsletter.
Or if you have a story idea, email us at email@example.com.