Giving evidence for a fourth day in the trial of Weatherston on a charge of murdering his subsequent girlfriend, Sophie Elliott, the witness said she answered Weatherston "grudgingly" when he asked her "and he became upset at my answer".
"He said to me, `I can't believe you'd tell me that; it's such an insensitive thing to say'," she told the court.
"So I walked into a trap."
To defence counsel Judith Ablett-Kerr QC, she agreed she had brought a calming influence to the relationship, that she was probably Weatherston's "bolt hole" and he could "sound off" in safe circumstances to her.
Questioned further by Crown counsel Robin Bates, about "the two different sides of Weatherston", the young woman recounted an incident when Weatherston was playing his guitar while she was trying to go to sleep.
She asked him several times to stop, eventually putting her hand on the guitar and suggesting he could play somewhere else in the flat.
He put down the guitar, got on the bed and jumped up and down on top of her several times.
"He just didn't stop. I told him `That really hurt'," she said.
Weatherston's response was, "Oh well, I was just playing at wrestling."
While she tried to give him the benefit of the doubt at the time, "it didn't seem to me he was playing", she said.
When she confronted Weatherston after another incident when he kicked her across the room and jumped on her, Weatherston said "it was the worst thing he'd ever done, to hurt me".
His immediate reaction at the time had been a combination of two things, "trying to blame me and being upset about it".
Asked about her comments Weatherston could be mean, the young woman said he had threatened to throw their cat, Soph, over the balcony.
But he said it was a joke.
He had also threatened to "unstuff" a soft toy she had kept from her childhood.
She told Mr Bates she thought Weatherston appeared not to take responsibility for disputes with economics department staff.
"He truly and honestly thought people had undermined him in the faculty and that it wasn't his fault."
He carried several grudges long term and "really couldn't get over those at all".
"He had no coping skills or ability to learn from those incidents," the witness said.
Weatherston was unpredictable at times and it was hard to know whether she would be coming home to someone who was very stressed or very happy.
At times, he could be a fairly insecure person.
He could be very mean and get worked up very easily.
"But I doubt others would have known, as I was his primary sounding board. He was only like that towards me," the witness said.
She did not really see him behave like that in public.
