Whitney Houston's Long Battle with Drug Addiction

In 2005, Cissy Houston knocked on the door of her daughter Whitney Houston's Atlanta home after her son Gary warned her the singer "was in trouble."

Though she had been long worried about her daughter — whom she called Nippy — and her drug use, nothing could have prepared her for the haunting scene inside where Whitney lived with former husband Bobby Brown and daughter Bobbi Kristina. "Somebody had spray-painted the walls, painting big, glaring eyes and strange faces," Cissy wrote in her 2013 memoir, Remembering Whitney. "They were evil eyes, staring out like a threat. And in another room, there was a big, framed photo of Nippy, Bobby and Krissi, but someone had cut Nippy's head right out of it."

When Whitney appeared at the top of the stairs, the once-stunning star who sold more than 170 million records and racked up six Grammys "looked like someone I didn't know," Cissy told PEOPLE in 2013. "I knew my daughter was in grave danger."

The star tragically died at 48 from accidental drowning (she was found to have cocaine in her system). The swirl of stories and drama — including her mother's book detailing her anger and anguish over Whitney's drug addiction and the later feud between the Brown and Houston families over Bobbi Kristina's hospitalization and death — has continued.

In his 2016 memoir Every Little Step, Brown opened up about their doomed love story and how drugs helped lead to their undoing.

"The drugs wasn't her," Brown said in a 2016 20/20 interview with Robin Roberts to promote his book. Revealing that he first saw Whitney taking cocaine just before she was to walk down the aisle at their 1992 wedding, a tearful Brown told Roberts, "She did drugs but the drugs didn't do her. She knew how to handle herself."

The Pressures of Fame

According to her friends and family, who PEOPLE interviewed at the time of her death, there were two Whitney Houstons: the dazzling pop princess groomed by Arista president Clive Davis, and the girl from Newark, New Jersey, who rebelled against pressures to be perfect by turning to drugs in her early 20s.

"There were a lot of expectations in terms of who she was and who people thought she was," a close family friend told PEOPLE in 2016. "I think not being able to be herself 100 percent was a hell of a burden for her to have to carry. Someone may look good on the outside, sturdy and strong . . . [but] on the inside, you have someone who had insecurities and family issues and emotional personal issues and struggles."

After Davis signed her to his label in 1985, she "had to do what he said, wear what he said to, sing what he wanted her to sing and act like a goody two shoes when she was really a down and dirty girl from Jersey," said a record executive who worked with her. "Whitney definitely resented that."

Added a music source: "Clive made her into a mainstream pop star and allowed all of her wildest dreams to come true, but being this massive pop star came at a price. She had to act a certain way in front of the cameras for the label. That wasn't the real Whitney."

A Life of Rebellion

Entering a romantic relationship with Brown (the two wed in 1992 and had an explosive marriage that ultimately ended in 2007) and using drugs were "her rebellion against it all," said the family friend. "There has to be some outlet. For her, it became drugs." According to a record executive who worked with the singer for years, Whitney "did drugs to escape her pain."

At first, she was able to keep her drug use hidden, but "things got worse and worse," says a family source. "Suddenly, when she was using, she had no idea who she was or who you were and she became angry and lashed out. We'd take turns checking on her in Atlanta when things were bad."

Surrounded by enablers who "allowed Whitney to do what she wanted to do," the star was quick to fire someone "if she felt you were not being cooperative on some level," revealed the family friend.

Family Rendered Helpless

When no one else was around, it was Houston's daughter Bobbi Kristina who looked after the singer. Once showing up at Houston's Atlanta house, the family source recalled a then 11- or 12-year-old Bobbi Kristina answering the door.

"Bobbi said Whitney wasn't feeling well so [she] put her to bed," recalled the family source. "I went upstairs to her bedroom and the room was a disaster." With piles of clothes and dirty dishes strewn about and Houston asleep in the midst of it all, the family source said, "It was the bedroom of a junkie."

Though she entered rehab multiple times throughout her adult life, Whitney struggled with addiction until it ultimately took her life.

"She was in pain from all the pressure she was facing and the pain from living almost a double life," said the record executive. "She was doing ridiculous amounts of hard drugs and sacrificed her God-given talents for that."

* With reporting by KC BAKER, STEVE HELLING and TIFFANY MCGEE