Calvin Harris Ended Relationship with Taylor Swift After Being 'Intimidated' by Her Success, Source Says

• Calvin Harris and Taylor Swift's relationship ended because the DJ was "intimidated" by her success, a friend of the singer tells PEOPLE.

• Multiple sources confirmed to PEOPLE on Wednesday that the couple had called it quits after 15 months, with another insider revealing that there was "no drama."

Calvin Harris and Taylor Swift's

"[Harris] said on multiple occasions that he was intimidated by Taylor, which is why he would not attend any events where she was being honored, or any award shows unless he was nominated," explains Swift's friend.

Harris, 32, was notably absent when Swift co-chaired the Met Gala last month, as well as at the Grammys ceremony in February, and when the "Bad Blood" singer accepted an award named after her at the May BMI Pop Awards.

But Swift is holding her head high, adds the pal. "Taylor is an independent young woman, and she realizes it will take a very secure man to handle her success," says her friend.

A source close to the DJ – whom sources confirm ultimately pulled the plug on the relationship – tells PEOPLE that the split "wasn't a shock" for Swift because the couple had ongoing issues. "They come from very different worlds," the source explains. "Taylor is used to being treated a certain way."

The Harris insider added that he didn't feel like the relationship was "leading anywhere."

Swift, 26, and Harris first began dating in March last year, making their official outing as a couple at the Billboard Music Awards one month later. Just three months ago, the couple went on a romantic tropical vacation to celebrate one year together.

"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," says the Harris source. "Taylor somewhat lacks real-life experience. They will not be getting back together."

Taylor and Calvin, before the breakup 

Regardless, the insider says that Harris still has high praise for his ex, noting that the Scottish star "very much admires her as a person and what she has been able to do with her career. This is what drew him to her in the first place."

"She works incredibly hard for things that she believes in," the Harris source says. He always saw that as an amazing quality. They are still friendly."

Swift spent time with her family in Nashville ahead of the news, and is getting support from longtime BFF Abigail Anderson.