Calvin Harris was "intimidated" by Taylor Swift's success.
Calvin Harris and Taylor Swift
The 32-year-old DJ dumped the 26-year-old singer last week after 15 months of dating and friends believe it would take a "very secure man" to handle a relationship with her.
A source told PEOPLE: "Calvin said on multiple occasions that he was intimidated by Taylor, which is why he would not attend any events where she was being honoured, or any award shows unless he was nominated.
"Taylor is an independent young woman, and she knows it will take a very secure man to handle her success.
"It wasn't an equal relationship. Their age difference might not be significant for many couples, but for them it was part of the problem too. Taylor somewhat lacks real-life experience. They will not be getting back together."
However, the former couple plan to remain friends despite their split.
The source said: "She works incredibly hard for things that she believes in. He always saw that as an amazing quality. They are still friendly."
Meanwhile, it was claimed that Calvin - who recently had to cancel a number of shows after being involved in a car accident - had been "losing interest" in the 'Bad Blood' hitmaker for some time before they split.
A source told E! News: "Adam really liked Taylor, she was not the type of girl he ever dates and he liked that. He liked how innocent Taylor was and that she had a good caring heart. Taylor's heart was more in it then he was. He started to lose interest over the past few months, but really tried to not just break up."
And the couple's respective working schedules also didn't help their romance.
The source added: "They were just not very compatible in different areas in their relationship. The touring and traveling didn't help. It seemed like they were more friends than lovers.
"Taylor and Adam had very different group of friends."
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