Here's Why Jessica Simpson and John Mayer's Relationship Was So Toxic

Jessica Simpson's much-awaited memoir, Open Book, hasn't been released yet (it's available for pre-order now with a February 4 release date), but it's already causing a stir. The former singer-turned-billionaire-business-mogul tells all about her marriage to first husband Nick Lachey, her anxiety over her career, and her years of self-medicating with drugs and alcohol to cope with the sexual abuse she'd suffered as a child.

Simpson, 39, also lifts the lid on her relationship with musician John Mayer, whom she first met in early 2005. Mayer told Simpson how much he admired a song she wrote called "With You," and he began to write to her. The letters quickly became more intimate. According to Simpson, Mayer told her "he wanted to have all of me or nothing."

"Again and again, he told me he was obsessed with me, sexually and emotionally," Simpson writes in her memoir. The star, who married Eric Johnson in 2014 and has three kids with him—daughter Maxwell, 7, son Ace, 6, and baby girl Birdie, 10 months—reveals that while Mayer made her feel powerful physically, she also felt insecure around him during their on-off relationship.

"I constantly worried that I wasn't smart enough for him," she writes. "He was so clever and treated conversation like a friendly competition that he had to win." Simpson was so afraid of disappointing Mayer, she even had a friend check her texts for grammar and spelling errors. At times of uncertainty, she writes, "My anxiety would spike and I would pour another drink. It was the start of me relying on alcohol to mask my nerves."

"He loved me in the way that he could and I loved that love for a very long time," she told PEOPLE. "Too long. And I went back and forth with it for a long time. But it did control me."

Simpson and Mayer's relationship might sound conflicted and turbulent. But it may go beyond that and qualify as emotionally abusive.

"One of the hallmarks of emotionally abusive and controlling relationships is obsession," former counselor Deborah J. Cohan, who is a professor of sociology at the University of South Carolina Beaufort and the author of Welcome to Wherever We Are: A Memoir of Family, Caregiving, and Redemption, tells Health. "Interestingly, we are living at a time when people are using the word obsession very loosely and to talk about things like being obsessed with a certain type of food, song, book, activity or clothing item."

"But when people who study intimacy in relationships think about issues of obsession, we are talking about attitudes and behaviors that are overwhelmingly intrusive—both for the person who is obsessed as well as the target of the obsession," she continues. "It's like a hostile takeover where we don't get any real breathing room or sense of spaciousness. And people need that to be able to thrive in a relationship."

An obsessive partner is a red flag, says Cohan, who has served as an expert consultant in cases of domestic violence, sexual assault, and sexual harassment. "If someone conveys that they are that involved, enmeshed, and thoroughly preoccupied with our every move and thought, this is not a compliment," she says. "It signals danger because it goes far beyond any sort of normal interest or jealousy and instead becomes possessiveness. Obsession conveys a willingness to not be respectful of another person's boundaries and to be excessive."

Some people are more vulnerable to getting into relationships with people who are obsessive, adds Cohan, such as people who have been victims of abuse. "They may not be used to getting attention and experiencing a sense of devotion, or only used to getting negative criticism, and so even if this kind of attention and devotion is ultimately warped and dangerous, it might initially seem to fulfill unmet needs."

And early experiences of traumatic abuse can create a lot of anxiety. "Abuse creates a sense of uneasiness and the experience of walking on eggshells, feeling like if you did do this or did not do that you could possibly avoid being hurt," says Cohan.

In her powerful memoir, Simpson reveals that she was sexually abused as a young girl by the daughter of a family friend, and during her 20s, tried to deal with the deep-rooted trauma with alcohol and stimulants. "I was killing myself with all the drinking and pills," she writes. But she's been sober since November 2017, after hitting rock bottom following a Halloween party at her home.

"When I finally said I needed help, it was like I was that little girl that found her calling again in life," she told PEOPLE. "I found direction and that was to walk straight ahead with no fear. Honesty is hard but it's the most rewarding thing we have. And getting to the other side of fear is beautiful."