The veteran singer told the Independent that at the time, the Democratic candidate George McGovern had lost the presidential election to Richard Nixon, and Lennon was very upset and got drunk.
Ono revealed that soon after, the pair was invited by activist Jerry Rubin invited to his apartment for a party and they went.
Ono said that Lennon was staggering around and went into another room and started making love to a woman.
The report claimed that the very next day, Lennon apologised and spoke of the love he had for her that could overcome such a meaningless, drunken act.
Ono asserted that she realized after the incident that it was not in Lennon's personality to behave like a normal partner and he must have been longing for his space.
Ono eventually asked the singer to go to LA, and do what he wants to do.
The couple separated for 18 months, during which Lennon had a relationship with his assistant May Pang, but in late 1974, they reunited, after which she became pregnant with their son Sean.
Ono recalled that it was great that she gave him that freedom and it was the logical choice.