The 20-year-old star, who was linked to Horan last year, said it has been impossible for them to stay in touch, reported Sun online.
Horan and Lovato first got friendly during the boyband's first tour of the US.
"Sadly as sweet as he is, it's hard to maintain a friendship with somebody you really can't hang out with without people automatically assuming you are dating," she said.
The 'X Factor' USA judge had previously admitted Horan was
her favourite out of all the One Direction boys.