Jerry Jones' longtime assistant, Marylyn Love, passed away this week ... and the Dallas Cowboys owner said he's devastated over the death, calling her his "best friend."
The team and Jones announced the sad news in a statement Thursday ... with Jerry saying he's flat-out heartbroken over it all.
"Marylyn has been by my side, she has been my rock, my voice, my calm in the storm for more than 40 years," Jones said ... "She was our foundation."
Jones said Love left a law firm in Oklahoma decades ago to become the Cowboys owner's assistant -- and the 79-year-old added that she helped form the Cowboys' org.