Gwyneth – who has two children, Apple, seven, and five-year-old Moses, with Chris – said: "Sometimes it’s hard being with someone for a long time. We go through periods that aren’t all rosy. I always say, life is long and you never know what’s going to happen."
And while the 38-year-old beauty says they have no intention to split up, she knows if they ever did it would be amicable because they have a lot of respect for each other.
She told America's Elle magazine: "If, God forbid, we were ever not to be together, I respect him so much as the father of my children.
"I made such a good choice. He’s such a good dad. You can never be relaxed or smug and think, 'I’ve got this thing.'
"That’s also part of it: keeping yourself on your toes. I’m not going to take this for granted."