The relationship apparently began with letters and phone calls, progressing to a face-to-face meeting just last week when she visited him in jail.
"She's going to be my future wife. We'll be laughing forever," the convicted murderer told the magazine.
"I'm happy. She treats me decent, she loves me. She's kind of spoiling me right now. I just want to be happy and enjoy my life. I think I did enough time."
Avery was charged in November 2005 with sexually assaulting and killing photographer Teresa Halbach, who disappeared that Halloween after travelling to his salvage yard to shoot photos for a car magazine.
Avery and his then 16-year-old nephew, Brendan Dassey, lived on the property. A jury in 2007 convicted Avery of being a party to first-degree intentional homicide and a judge sentenced him to life in prison.
He has always maintained that he was framed for the crime.
Brendan Dassey, 16, is escorted out of a Manitowoc County Circuit courtroom in Manitowoc, Wisconsin. Photo / Supplied
Later that year, a separate jury convicted Dassey of being party to first-degree intentional homicide, mutilating a corpse and sexual assault.
He, too, was sentenced to life - though his conviction was sensationally overturned this year.
The case has long captivated the public. Just two years before Halbach's death, Avery had been released from prison after spending 18 years behind bars for rape that a DNA test later showed he didn't commit.
The creators of the original series Making A Murderer, which documented the case, are now working on a second season.
