Sean Ono Lennon Says Mom Yoko Ono 'Never Has Moved on' from Her Relationship with John Lennon

• Sean Ono Lennon says mom Yoko is still grieving her husband, John Lennon
• Sean says Yoko "never has moved on from that relationship" with John
• John was shot and killed in New York City in December 1980

This week marks 44 years since John Lennon’s tragic death — and his son Sean Ono Lennon says the late Beatle’s wife Yoko Ono is still not over the devastating loss.

Sean, 49, told BBC Radio 6 Music that Yoko, 91, spoke of John “every day” after he was shot and killed in New York City on Dec. 8, 1980 at age 40.

“I grew up with my mom speaking about my dad every day. She famously cut her hair when my dad died [because] in Japan, you used to cut your hair when your husband dies,” he said. “So she spoke of him every day and I think she never has moved on from that relationship.”

Sean — who recently helmed a reissue of John’s 1973 album Mind Games — also spoke candidly of John’s famous “Lost Weekend,” an 18-month separation between his parents during which John lived with May Pang. It was during that time apart that John released and recorded Mind Games — but to Sean, his parents, who married in 1969, never really split (After John’s death, Yoko went on to date interior designer Sam Havadtoy, though PEOPLE previously reported that they split in 2001).

“The truth is, even when they were apart, they were always talking. So I don’t think they ever really broke up. All his stuff was still in the apartment with my mom. It’s not like they had a real separation,” he said. “I think it’s clear what his view of my mom was in his life. She was monumental, obviously, and the whole album is about her. She’s there in the studio… It sort of confirmed how deeply in love he was with my mom.”

Sean, who became a musician himself, added to the BBC that he’s spoken to Yoko about the “Lost Weekend,” and said she still has “bad feelings” about the time, but knew that in order for the relationship to survive, she and John needed a break.

“I think every relationship is very difficult, and I don’t believe that human beings have really solved the love equation,” he said. “So I think they did the best of anyone I can see.”

Sean recently opened up to PEOPLE about his parents’ relationship, and said John’s “entire life and art was infused with his relationship with my mom.”

“The whole album is about my mom. They’re mostly love songs about her,” he said. “My dad declared to the world that ‘John and Yoko’ were one word. I think he always had his heart set on her. He was so in love with her. They had a legendary love and I think that this album is infused with that love. You can hear it.”

He also explained that his decision to become a musician wasn’t because he had a particular passion for it, but because it helped him feel close to his late father.

“I never played music because I was good at it. I lost my father and I didn’t know how to fill that void. Learning how to play his songs on guitar was a way to process the loss as an activity that made me feel connected to him,” he said. “When you’ve lost a parent, things like that motivate you — because you’re trying to find them. Making music always made me feel like I was getting to know him better.”