The One Direction singer – who started dating the Xtra Factor presenter in October – has reassured the TV star that he isn’t worried about the age gap.
And the boyband member said he won’t give in o criticisms of their romance.
A source said: “Harry’s absolutely head over heels with Caroline and keeps telling her so.
“But obviously all the hassle their relationship’s had and the fact that he’s a teenager on tour surrounded by young girls has left her feeling uneasy.
“However, Harry’s assured Caroline there won’t be any partying on the One Direction tour. He just has no interest.
“He can’t believe his luck that he is dating Caroline and is going out of his way to show her how he loves her. He spoilt her rotten with gifts including a Mulberry bag.”
Though she is happy, Flack, 32, has reportedly told Styles, 17, he should consider getting a girlfriend his own age but he only has eyes for her.
The source told Now magazine: “She’s told him he should be with a girl his own age but he doesn’t listen.
“She even confided that she doesn’t think they’ll last beyond the summer. She does care deeply for him – he makes her laugh.”