The musician, who just released his new solo album, McCartney III, told CBS Sunday Morning: “I occasionally will have thoughts: why don’t I just break down crying every day? Because it’s that bad.”
“There will be times when I have memories and think, oh my god. It was so senseless,” he added.
McCartney said that, were Lennon still alive today, he would certainly still be writing music.
“He was showing no signs of slowing up. He was still making great music,” he said. “The question is: would we have ever got back together again? I don’t know. We don’t know.”
“We were friends,” he continued. “That was one of the great things about it. I don’t know how I would have dealt with it. I don’t think I’ve dealt with it very well. I wouldn’t be surprised if a psychiatrist would sort of find out I was slightly in denial. Because it’s too much.”
In another recent interview, McCartney revealed that it was only after The Beatles song “Help!” was released that he realised Lennon was actually struggling.
Elsewhere in the CBS interview, he criticised people who claim that being asked to wear a face mask is an infringement on their civil liberties.
“When people sort of say, ‘Wearing masks is infringing on my civil liberties,’ I say, ‘No. That is stupid,’” he remarked.
McCartney has been vocal during the coronavirus pandemic in urging people to take precautions to protect themselves and their loved ones.
Over the weekend, prime minister Boris Johnson announced a new Tier 4 level of restrictions to prevent the spread of the virus.
Residents of London, the south east and east of England are required to follow a strict set of rules until at least 30 December, after spikes of Covid-19 infections.