People gave Ono a lot of shit for following Lennon to band practices (a taboo in the music world known as "being a Yoko Ono"), but Ono only did that because Lennon demanded that she come out of fear she would leave him. He even made her go into the bathroom with him, afraid someone would snatch her away while she waited in the lobby. At the same time, he was openly unfaithful to her, just as he was to his first wife.
In the end, though, the biggest target of Lennon's cruelty was his son Julian. Lennon was absent for most of Julian's life, and the time he spent with him often led to yelling, insults, and very uncomfortable situations.
Lennon stated in an interview that Julian was unplanned and "came from a bottle of whiskey." Lennon did admit his failings near the end of his life, but he added, "I will have to be a lot older before I can face in public how I treated women as a youngster." Sadly, that didn't happen, so he died an asshole