REDWOOD CITY, California (CNN) -- The woman who introduced Scott Peterson to his eventual mistress testified Wednesday in Peterson's double murder trial that when she first met him, Peterson never mentioned being married.
Shawn Sibley also testified that Peterson talked constantly about sex but said he was looking for a "long-term relationship."
Prosecutors have charged Peterson, 31, with murdering his pregnant wife, Laci, and their unborn son, sometime on December 23 or 24, 2002.
Prosecutors are trying to establish that Peterson's affair was the motive for the slaying.
Sibley said she met Peterson at a business conference in October 2002. Sibley -- who was engaged at the time -- said Peterson told her he had "lost" the woman that he believed "was his soulmate" and asked her if she thought that meant he was destined to be alone for the rest of his life.
"He said he hadn't been successful in finding anyone and wanted a long-term relationship. As I got to know him I began to think he was serious," Sibley testified.
Sibley said that after Peterson asked her if she had any "single friends," she thought of Amber Frey, but warned him that Frey had had bad luck with men and was looking for a serious relationship.
Peterson "was very interested in meeting her" and asked whether she was smart and what she looked like, Sibley said.
She said that on December 6 -- after Frey and Peterson began dating -- Sibley found out that Peterson was married and confronted him in a phone call, but he denied it.
Later, Peterson called Sibley back, "sobbing hysterically saying he was sorry he lied, but that he lost his wife," she testified.
Once again, he denied being married and said he wanted to tell Frey himself, said Sibley. He later reported to her that he had told Frey and "he said he couldn't believe how great she was for forgiving him."
Sibley said on December 29, 2002, someone called Frey to tell her that Peterson was the husband of the missing pregnant Modesto housewife, Laci Peterson.
Sibley also testified that Peterson was thinking of having the initials "H.B." added to his business card, which she said stands for "Horny Bastard."
Talking about sex "was a constant thing with him, he always brought it up," she said.