The 29-year-old explained that since moving into the film director's house, the pair have enjoyed cooking together.
Ainsley told Tatler: "We are both really low-key people and what we love to do is stay in and cook together and just hang out.
"I wear red lipstick when I'm doing the washing-up. It's hot - you should try it."
The model insisted that the decision to live together was something that happened naturally as they spent so much time with each other.
She said: "I don't think there was really an official moment - no huge conversation or anything strange - we just wanted to spend time together and I was there all the time and evenings after work so it just kind of happened."
Ainsley also commented that the 42-year-old's children with former wife Madonna are "beautiful" but admitted that she is hesitant to talk about them.
She added: "They are beautiful boys and I feel really lucky that I know them. If they were my boys, I'd talk to you about them all day but certain things must be private."