Katie Holmes was scared she was turning "into a robot" while with Tom Cruise.
The former Dawson's Creek actress — who has filed for divorce from the Rock of Ages star after five years of marriage — felt like she had changed "so much" in her time with Tom and found their relationship had become "too much" for her.
A source said: "After five years of this Katie really felt like she was going crazy and that she was actually turning into the robot that the press had always made her out to be. Katie has actually got a great personality and she used to be spunky and feisty. She changed so much when she was with Tom, she became downtrodden and insipid.
"In the end it just got too much, she was sick of it and decided she had to do something. Basically, she grew up and lost the starstruck goggles she had been wearing."
Holmes is reportedly seeking full custody of their six-year-old daughter Suri, and began to question her life with Cruise and how much he made decisions.
The source added to RadarOnline.com: "Katie did not want Tom making all the decisions in Suri's life, and that's what was going on. She decided it was high time she started deciding on what was best for her daughter, or at least having an equal say, and she knew that would be impossible if she remained Mrs Tom Cruise."
Get more on the split: