Stephanie, 41, was found upstairs, lying on a blood soaked mattress, with extensive bruising and injuries across her face and body, the trial heard, and Devenport was later arrested.
A post-mortem examination found 102 injuries including to her brain, fractures which are often associated with strangulation or mechanical asphyxiation and severe facial bruising.
The couple had met about a year before her death while both were receiving support for alcohol addiction.
Police inquiries revealed Stephanie had not left the house for about 10 days before her death, during which time Devenport had been feeding her largely on alcohol and ice lollies, the CPS said.
Det Insp Andrea Price said: “Stephanie’s family described her as a fun-loving, caring, beautiful girl, and my thoughts are with them as they continue to come to terms with such a loss.
“No parent should ever have to go through the pain of losing a child, nor should they have to sit and relive that trauma by way of a trial.
“Devenport was a coward, he has shown no remorse for his actions and throughout the investigation he has refused to admit what he did.”