Kate Greville was asked at Giggs' trial why she moved into the former Welsh international's home during the first Covid-19 lockdown if "he had been a serial and violent abuser".
She said: "It was a cycle of abuse that made me feel insecure," and later added: "I kept going back, he kept promising the world."
Her voice broke as she told the jury: "He made me believe that he would not do it again and, stupidly, I went back. I am hugely ashamed of that, but I did."
Giggs, 48, denies using controlling and coercive behaviour against Ms Greville between August 2017 and November 2020, assaulting her, causing actual bodily harm, and the common assault of her younger sister.
Jurors at Manchester Crown Court heard that PR executive Ms Greville, 36, had described living with the defendant during the first Covid-19 lockdown from March 2020 as "utter hell".
The pair moved in together for the first time after Giggs asked her to live with him at his property in Worsley, Greater Manchester, she said.
On Thursday, Chris Daw QC, defending, continued his cross-examination of Ms Greville, asking her: "Could you have gone to your parents or someone else?"
Ms Greville replied: "Yes."
Mr Daw said: "Was one of the reasons you didn't because actually you wanted to spend time with Ryan in his rather larger house?"
The witness said: "I wanted to stay with Ryan, not because of his house but because we had just started the relationship again."
Mr Daw said: "Can I suggest that you would not have done that if he had been a serial and violent abuser?"
The barrister played to the jury of seven women and two men two videos of the couple in lockdown - one in which they exercised together in the garden and the other rapping along to 50 Cent's In Da Club.
Mr Daw put it to Ms Greville that lockdown was obviously hard but the pair were doing normal things "much of the time" and having fun.
Ms Greville said: "It was not all fun. It doesn't mean he was being nice to me all the time.
"At the start of lockdown it was fine but it got progressively worse."
During lockdown, the couple also took part in online family quizzes, wine tasting on Zoom and had Michelin-starred chefs bring in food, the court heard.
But Ms Greville said there were arguments, including one involving loading the dishwasher.
Mr Daw said: "You suggest in your various accounts that lockdown was a period of living hell."
Ms Greville replied: "I felt like I was losing my mind. I was having panic attacks. It was a horrific time for me."
Earlier this week, Ms Greville told a jury that Giggs grabbed her by the shoulders and headbutted her in November 2020 after she confronted him about his serial cheating.
In the lead up to the alleged attack, she said she learned he had "full-on relationships" with eight women while they were together.
On Thursday, Mr Daw said to Ms Greville: "I suggest to you that decision (to leave him) was entirely based on that issue, that infidelity. It was nothing to do with coercion, violence, anything like that."
Ms Greville replied: "There's a lot of emails between me and him where I say a lot more things about the control and coercion and manipulation."
She said it was "incorrect" that her decision to leave Giggs was solely because "he was a cheat".
Mr Daw asked whether finding out Giggs was involved with other women made her decide she "needed to come up with a plan".
Ms Greville told the court: "I needed a plan to get away in secret so he couldn't find me, so he wouldn't harass me. And how to let him know how I had found all those things out."
She agreed with Mr Daw that Giggs was "very flirtatious with women" and "got a lot of attention out and about in all sorts of situations, from both men and women, because he's well known".
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