Complex sentence: After Lennon began a relationship with Yoko Ono, and Apple started to founder as the group grew apart, Shotton parted company with Lennon and the Beatles, resuming management of the Hayling Island supermarket, which he continued to run until the late 1970s.
Split into simpler sentences: After Lennon began a relationship with Yoko Ono and Apple started to founder, Shotton parted company with Lennon and the Beatles. He resumed management of the Hayling Island supermarket, which he continued to run until the late 1970s.