According to Morgan Spurlock, the filmmaker who travelled with One Direction to create their 2013 documentary 'This Is Us', the 22-year-old singer found it difficult being away from his family and friends, especially his fiancee, Little Mix star Perrie, to whom he proposed shortly before the movie's premiere.
He said of Zayn's decision to quit the band last week: ''I think he was the one who struggled with it the most.
''And being away, being on the road, being away from his girlfriend I think finally just got to him, and I think he said, 'I'm done'.''
As well as missing the blonde beauty, Morgan also believes Zayn - who found fame with the group on 'The X Factor' in 2010 - was interested in pursuing other creative hobbies and often spent time drawing in his free time during the tour.
The director told the Huffington Post: ''He wanted nothing more than to sit in his house and spray paint and draw and do art, and I think this explosion that happened to him - which was something none of them ever predicted - [was hard]'.''
Meanwhile, the couple - whose relationship was recently rocked by cheating rumours - jetted off on holiday with Zayn's family, including his sisters and mother, earlier this week.
They were spotted boarding a private jet in the UK with a small number of people and it is not yet known where the group have flown to, but the girls were spotted shopping for shorts and dresses in preparation for the trip.
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