In an interview on ITV's Lorraine, Richard revealed that he had a hard time coming to terms with her death in 2015.
He said: "She died because she had an accident. You can't plan what's going to happen in that respect."
The TV presenter and singer suffered a stroke after having a fall at her home in Spain.
Sir Cliff said that the timing of her death was particularly hard because it was before the abuse allegations against him were dropped.
"I was distraught," the singer recalled, "When you go to your bed you're on your own and that's when I became really dependent on God."
In the interview, Richard also shared happy memories he had with Cilla, including the time shared on holiday in Barbados.
"She just made me laugh. She was full of fun," she said.