The Formula 1 driver and the 'x factor' judge recently split after four years together but Lewis is desperate for them to get back together so has been proving his love for her.
A source told the Daily Star newspaper: "Lewis is on a full-on mission to get Nicole back. He's been having her favourite flowers and thoughtful gifts delivered to her LA home and to the set of 'X Factor'.
"He's also been sending her notes, saying, 'I Love you. I want you back.' He misses her terribly and has told friends he won't stop until he's won her over."
However, Nicole, 33, isn't sure if she wants to reunite with her 26-year-old former beau.
The source added: "She is enjoying having the control at the moment, although she has yet to make her mind up. She has been hit hard by split."
After the pair's split, Lewis admitted he still had "very, very strong feelings" for Nicole and he was hopeful they could rekindle their romance at some point in the future.
He said: "We still have very, very strong feelings for each other and I still love her very much. Who knows, maybe we will be together in the future?
"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."
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