Bret Matz admitted to killing his “lover, his baby, his boy” by cracking the back of his head several times with a nearly 5-pound lamp in the troubled couple’s Monte Rio home in January, Deputy District Attorney Robert Waner told a Sonoma County jury this morning.Robert Guess died of multiple blunt-force wounds to the head “within seconds,” Waner said in his opening statement at Matz’s murder trial in Sonoma County Superior Court.Waner said Matz remained in the house at 9066 Middle Terrace Road for several hours before wandering into town. He was “intoxicated, overwrought, agitated and grieving,” but he admitted to a number of people he encountered that he killed Guess, Waner said. Deputy Public Defender Jenny Andrews told the jury that Matz did admit to the killing but that both he and the 46-year-old victim struggled with alcohol abuse during their volatile relationship. Monte Rio residents had noticed both of both of them had black eyes as they strolled through town days before the Jan. 2 murder, Andrews said. Matz was arrested in September 2008 on suspicion of assaulting Guess. His trial was scheduled for December — a month before the killing — but the case was dismissed when Guess refused to cooperate and let a restraining order expire, according to court records.On Jan. 2, a hysterical and intoxicated Matz told a the owner of a local boutique that he had killed Guess. The storeowner contacted authorities.Monte Rio Fire Department personnel found Matz leaning over a guardrail on Middle Terrace Road, about 60 feet above the fire station. They believed he was about to jump, the Sonoma County Sheriff’s Department said. Matz told fire department personnel he killed his roommate, and they found Guess’s body in a bedroom of the home.Andrews told the jury they won’t hear evidence that Matz intended to kill Guess and that she’s confident the panel will find him not guilty of pre-meditated, first-degree murder.The trial is before Judge Julie Conger.