"Harry and Taylor had an incredibly intense relationship, and really did care strongly about one another. Sadly it fizzled out just as quickly, and came to a head following a series of angry spats on holiday," a source told contactmusic.com.
"Harry felt Taylor was nagging him, quizzing him on his intentions with various women and generally having very little faith in him.
"It all became too much and Harry found her a little too demanding. Taylor probably engineered the split but Harry held all the cards in the relationship," added the source.
However, sources close to Styles, who was comforted by another girl just 24 hours after being dumped by Swift, has not ruled at a reconciliation once they have spent some time away from each other.
"They are having a break for the moment to cool off. But who knows what the future holds?
"They're both young and hugely successful, with the world at their feet," said another source.