The Pussaycat Dolls beauty and the Formula One racing driver - who have been dating for two years - reportedly split up last week because Lewis felt he was being pressured into marriage.
A source told Britain's Sunday Mirror newspaper: "Lewis was adamant the relationship had come to an end. He was feeling under pressure to take their union to the next level and he wasn't wanting to become engaged, get married or think about having children.
"He's young, they spend an awful lot of time apart and he's just not ready to leave his youth behind for a lifetime with Nicole."
The 31-year-old beauty is reportedly devastated by the split.
The source added: "Nicole's mortified - she imagined being with Lewis for a long time and she's shocked that things have ended so suddenly.
Another insider added: "She's very upset about being ditched and needs time out. She's cleared her schedule and will be in Los Angeles for the next two weeks."
The 24-year-old British racer - who is worth an estimated Â£75 million - is said want to date other women and enjoy being single.
Another source said: "He wants to play the singles market for a while and enjoy himself."
In a clear echo of Frozen, this Disney animated adventure centres on a fiercely independent...
British pop heartthrobs One Direction became a worldwide sensation when they were thrust together on...
Agents K and J work for the Men In Black, an organisation specialising in hunting...