The 27-year-old singer split up with James, 31, who she has been dating for almost a year, amid fears he wasn't as committed to the relationship as her and just wanted to raise his profile, reported Daily Mirror.
"Jessie fell hard for Luke, but over the summer she started having doubts," a source said.
James has already stopped following Jessie on Twitter and later Jessie posted a motivational message on the micro-blogging site.
She wrote: "You got this girl. You are stronger than you think x."