Lennon and Ono decided to reconcile early in 1975 , and became the parents of Sean Lennon . Lennon and Ono were having marital problems and decided to separate , and Ono suggested to Pang that she become Lennon 's companion . Ono explained that she and Lennon were not getting along , had been arguing and were growing apart , and said that Lennon would start seeing other women .