The 33-year-old singer and the 26-year-old Formula 1 driver recently called time on their four year relationship and although their hectic schedules were thought to be to blame, friends have revealed Lewis' reluctance to settle down caused the split.
A source said: "Lewis decided they had to part, she wanted more than he could offer at this stage in his life."
Nicole is reportedly devastated about the break-up of their relationship, even asking for time off from filming the US 'x factor' but show bosses have said no because they have are currently working on the live shows.
The source added to the Daily Mirror newspaper: "Nicole's asked for time off given everything that's happened, but her busy schedule just didn't allow it.
"She's completely devastated but has no choice other than sticking a big smile on her face and going about her engagements."
Meanwhile, Lewis has insisted the pair will remain friends and says he feels "pretty good".
He said: "We're friends and we can move forward. These times are sent to try you, it's about how you pull through. I have my family who are helping, so I feel pretty good."