EXCLUSIVE: Inside Johnny Depp & Amber Heard's 'Volatile' Relationship and When It All Went Wrong

Amber Heard and Johnny Depp have been on the rocks almost since their marriage started, sources tell ET.

Although Amber Heard filed for divorce from Johnny Depp on Monday after a year of marriage, sources tell ET their relationship actually started souring almost immediately after their February 2015 wedding in the Bahamas.

Heard, 30, and Depp, 52, fought "all the time," a source tells ET, and one alleged big issue between the two of them, according to the source, was the actress' former close circle of friends. Heard has always been open about her bisexuality -- coming out publicly at a GLAAD event in 2010 -- and previously dated photographer Tasya van Ree. According to the source, Depp was uncomfortable with Heard hanging out with her old group -- including van Ree -- and as a result, she distanced herself from her friends.

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Their 22-year age difference apparently didn't help things either. Heard and Depp met during filming 2011's The Rum Diary, but didn't come out as a couple until 2012, after he split with his girlfriend of 14 years, model Vanessa Paradis.

"She is really young and affected by the industry and scene at times," the source says. "She is a cool girl, but Johnny is cooler and doesn't tolerate that."

The couple initially hit a rough patch in May 2015, according to the source, but they decided to give the relationship another shot, at least for a year.

"She can change her mind within minutes," another source tells ET. "One minute they are off and the next she decides she wants to stay. The marriage has been on the rocks since it started."

Heard and Depp appeared unhappy together as far back as last September, when they attended the actress' The Danish Girl premiere at the Toronto International Film Festival and got into an argument on the way home, the same source tells ET.

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However, Heard denied reports of marital problems between the two last November.

"I try not to react to the horrible misrepresentation of our lives, but it is strange, and hard," she told Marie Claire.

Still, the exes' split is apparently no surprise to the former couple's friends.

"They have been having problems for quite some time," one source tells ET. "It started a few months after they got married and it just never got better. It was extremely volatile."

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The two kept their finances separate during their marriage, the source also notes. However, Heard is now asking for spousal support from Depp.

Heard and Depp never signed a prenuptial agreement.

On Wednesday, Depp filed a response to his ex's divorce filing, asking the court to "terminate the court's ability to award support" to Heard, according to court docs obtained by ET.

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