The former Pussycat Dolls singer's position on the UK talent show is up in the air, but it is understood that Hamilton is worried that they will spend too much time apart if she signs up for another series.
"Lewis has said to Nicole this is going to be an awful situation and perhaps she shouldn't do it," a source told the Sunday People.
"If he thought she had her heart set on returninghe wouldn't say this, but he knows she isn't desperate to go back and thinks she would be happier if they were together.
"Nicole is also worried she won't see much of Lewis so it is a big factor that will deeply affect her decision."
The couple are thought to have previously split temporarily due to their busy schedules.