Genevieve Cook kept a diary throughout their year-long relationship, and provided her journals to David Maraniss of the Washington Post, whose biography "Barack Obama: The Story" will be published next month.
Cook's description of a 22-year-old Obama isn't surprising given his political persona: she complains frequently of his emotional distance, cool detachment and caution during their relationship in 1984.
"Barack — still intrigues me, but so much going on beneath the surface, out of reach. Guarded, controlled," she wrote in one of several entries, this one from March of that year, shortly after the couple met at a party in New York after Obama attended Columbia University.
In another entry, she noted: "The sexual warmth is definitely there — but the rest of it has sharp edges, and I'm finding it all unsettling and finding myself wanting to withdraw from it all.
"I have to admit that I am feeling anger at him for some reason, multi-stranded reasons. His warmth can be deceptive. Though he speaks sweet words and can be open and trusting, there is also that coolness."
She also wonders: "How is he so old already, at the age of 22?"
The award-winning Maraniss, who asked the president questions about Cook in an Oval Office interview as he researched his book, writes that the inter-racial couple discussed race often as Obama struggled to find a sense of belonging.
"She sympathized and encouraged his search for identity. If she felt like an outsider, he was a double outsider, racial and cross-cultural. He looked black, but was he?" Maraniss writes.
"He confessed to her that at times 'he felt like an impostor. Because he was so white. There was hardly a black bone in his body.' At some point that summer she realized that, 'in his own quest to resolve his ambivalence about black and white, it became very, very clear to me that he needed to go black.'"
She wrote in her journal of Obama's fantasy woman: "I can't help thinking that what he would really want, be powerfully drawn to, was a woman, very strong, very upright, a fighter, a laugher, well-experienced — a black woman, I keep seeing her as."
The future president met his wife, Michelle, a few years after his relationship with Cook ended.
Maraniss describes Obama's years in New York as "the most existential stretch of his life." In an interview with Vanity Fair, he describes asking Obama about his exes.
"Barack Obama did not read the journal entries from Genevieve Cook, but during my interview with him we discussed some of them," he said. "He was, of course, curious about her, where she was, and how she was doing."
Obama also admitted to Maraniss that during those years in New York, he was "'deep inside my own head … in a way that, in retrospect, I don't think was real healthy.'"
Obama lived briefly with Cook before their breakup, and her entries are filled with sweet details about their domestic life together, including his penchant for the New York Times crossword puzzle every Sunday morning.
He wrote of Cook, not by name, in his own autobiography "Dreams of My Father," but told Maraniss that he combined several ex-girlfriends in his memoirs to protect their identities.
Cook isn't the only girlfriend in Maraniss's book; there's another, an Occidental University student and literary magazine editor. Letters between Obama and Alex McNear, however, focused on philosophy and literature, while his subsequent relationship with Cook was more romantic.
Obama's breakup with Cook ended much as it had proceeded — calmly and cautiously.
"Barack leaving my life — at least as far as being lovers goes," Cook wrote.
"In the same way that the relationship was founded on calculated boundaries and carefully, rationally considered developments, it seems to be ending along coolly considered lines."