A Sonoma County jury convicted Bret Matz this afternoon of the second-degree murder of his lover, Robert Guess, in the couple’s Monte Rio home on Jan. 1, 2008. Matz, 47, showed no visible reaction when the jury returned its verdict after its second day of deliberations. A sentencing date may be set in court on Friday.Matz admitted during his testimony that he was drunk when he killed 46-year-old Guess in their Monte Rio home on Jan. 1 by hitting him three times in the head with a four-pound table lamp. Guess also was intoxicated at the time of his death, according to testimony in the trial.Deputy Public Defender Jenny Andrews told the jury during her closing argument that the couple had a history of violent confrontations, and that Matz acted in self-defense, fearing for his life.She told the jury that if they believe Matz acted in self-defense, they must acquit him of all charges including manslaughter.Deputy District Attorney Robert Waner argued the murder was “the final act of a tumultuous relationship” in which Matz acted with implied malice. Waner had pressed the jury to return a first-degree murder conviction.