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.

The couple tied the knot in 2003 while Menendez was serving time for the 1989 murders of his and his brother Erik's parents.

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,