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Johnny Depp and Amber Heard had only been married for 15 months when she filed for divorce on Monday, but a source close to the actress says she felt it was a necessary step after months of strife.

"Amber did what she had to do to take care of herself," the Heard source tells PEOPLE.

Tension between the couple started even before they wed, with a source telling PEOPLE Heard expressed hesitation about settling down with the actor 22 years her senior at their engagement party in March 2014, two months after their engagement.

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"Before Amber met Johnny she was just a regular super cool hipster chick living with roommates who dated girls," a source tells PEOPLE. "At their engagement party she kind of got cold feet ... she was just like what is this scene and what am I doing here? She kind of couldn\'t believe it was her life now."

In December 2014, a source told PEOPLE there "is turmoil in the relationship" and wasn\'t sure if and when they would wed.

The couple eventually tied the knot in February of last year. Depp, 52, was not present when she rang in her 30th birthday this past April in Palm Springs.

Heard\'s filing came just three days after the death of Depp\'s beloved mother, Betty Sue Palmer, at 83.

Although the couple never spoke publicly about any discord, Heard acknowledged rumors about the state of their union while speaking with

"I try not to react to the horrible misrepresentation of our lives," she said. "But it is strange and hard."

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