The Pushing Daisies actress parted ways from Harry Potter star Thewlis last December (10) after 10 years together, and in a new interview with Tatler magazine, Friel lifts the lid on the breakdown of their romance.
She says, "We spent 10 wonderful years together. And then we both just decided that we'd become friends as opposed to lovers.
"I thought the relationship would last forever, but as you get older you realise that certain relationships are for certain times."
The former couple shares a daughter, Gracie, and the youngster has embraced her mother's new boyfriend, actor Rhys Ifans, who the actress met while working on movie Neverland.
Friel adds, "He is brilliant with Gracie. We introduced her to the idea really gently and softly. The good thing is, she had seen him on the set of Neverland and she said, 'You are very nice friends. I think he's very nice.'"
Detailing her home life in Windsor, England with Ifans, Friel says, "We cook together. We often have midnight cook-offs if we've been out and we're both hungry... We hardly watch TV but if we do it's loads of cookery and travel programmes.
"I think one of the things that draws us together so much is our need to feel safe. You know, everyone has to go out there and face the massive wide world and face rejection and it's nice to have a sanctuary and a place to go and a pair of big arms around you and someone to say, 'Oh, you're all right.'"