A May-December romance that ended in murder has earned a Fort Worth woman a ten-year prison stretch.  Robin Mirth is now 54 and admits she murdered her 86-year-old husband last year.  In May of 2009, Fort Worth police found Robert Stevenson shot dead in his home and then found Mirth hiding behind some furniture.  They also found the shotgun believed to be the murder weapon.  Acknowledging that ten years might seem a light sentence for murder, Tarrant County prosecutors say the victim’s family approved the deal because it eliminated a trial during which some dirty laundry about the couple’s relationship would no doubt be aired.  The couple had been together for 25 years.  She was in her late 20’s when they married and he was nearly 60.