Lyle Menendez and his wife, Rebecca Sneed, quietly ended their marriage after more than 21 years together, but she remains a key figure in his life despite rumors of a cheating scandal Sneed says are baseless, PEOPLE has learned.

Lyle Menendez, 56, is just moving on fast from behind bars. The infamous prisoner, who was convicted in 1996 alongside his brother, Erik Menendez, for the 1989 double murders of their parents, Jose and Kitty Menendez,