Ricardo Cruz, now 34, had known Honey Vitagliano, 31, since high school and the two began to date several years later.
But although he showered her with expensive gifts including $900 pair of diamond earrings, and took her on several outings to upscale restaurants and a Mendocino Coast resort, she made it clear she was not her boyfriend.
She told a Santa Rosa CA, court: "He spent a ridiculous amount of money for someone who wasn't a boyfriend, but I went along. It was a good time."
She added that Cruz made a habit of calling her mom Kathryn, 55, for relationship advice and would go round while she was at work.
Then a few weeks before her mom was viciously stabbed to death, she broke things off with Cruz and he continually called her.
But after the murder he stopped calling although it didn't immediately occur to her that he may be a suspect.
Cops initially focused on her ex, but after they obtained a voluntary DNA sample from Cruz last year, they found it was a perfect match for DNA sample taken from a scraping of one of Vitagliano's fingernails after her death.
Cruz who is denying murder, remains in Solano County Jail custody with bail set at $1 million.