She didn’t recognize it at the time, and today her ex emphatically denies that he abused her in any way—two things that underscore the difficulty of noticing, from the inside, when a relationship becomes traumatic for one of the people in it.

To try to understand this phenomenon, I interviewed Lauren, her ex, and several of their friends, and I reviewed extensive transcripts of Google chats between Lauren and her friends at the time she and her ex were dating. Lauren hopes her story can help others avoid similar pain. For privacy, she asked The Atlantic not to use her full name, and her ex asked not to be named at all.

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They met when Lauren, her middle name, was in her mid-20s and her ex was nearly 30. He was her first serious boyfriend. They had run in the same circles for years, but when he moved to New York for work, they reconnected. He was of medium height, and balding, but cute. With degrees from prestigious universities, he looked great on paper. Lauren was fresh off a string of disastrous dates. He made a move; she went with it.

At first, he made Lauren laugh and impressed her friends. He even planned a romantic weekend at the beach and took Lauren to Costa Rica.

But before long, Lauren said, he began making obnoxious comments, boasting about his ex-girlfriends and saying things like, “I could walk down Central Park West and get any girl I wanted,” Lauren said. (Her ex denied this.)

“I sort of let it slide because I was so happy to be in a relationship with someone who I thought was otherwise right for me,” Lauren told me. “In retrospect, they were harbingers of worse to come.”

What was to come, according to Lauren, was a gauntlet of near-daily put-downs about everything from her appearance to the way she poured water into the sink. As her self-confidence evaporated, she found herself wondering if she could do any better.

Lauren thought if she just worked harder, she could fix the relationship. Relatively early on, the couple was clashing over trivial things, like gifts. When he won an award, Lauren coordinated a surprise party for him. To her ex, it was thoughtless, she said. She should have realized that his friends, who didn’t win the award, would feel bad attending such a party. Indeed, he told me, he wasn’t thrilled about it, although he did appreciate other gifts she gave him, and he told her so.

Another time, Lauren signed up for dance lessons to surprise him. Her ex had told her, “I’m bad at following,” she wrote to one friend over Gchat. “I keep trying to lead, or at least do my own thing. Damn independent streak of mine.” When she told him about the lessons, she claims he said she should have been at work instead.

For their second anniversary, Lauren devised a game in which they would each say what they loved about the other person. Her ex said he loved that Lauren was always trying to improve herself.