Mary Cosby went back to work pretty soon after her son, Robert Cosby Jr., passed away … and she’s now revealing she had to compartmentalize her life to get through it.

The new season of “The Real Housewives of Salt Lake City” is out now … and fans are seeing Mary deal with Robert’s shocking death … with a new scene showing her just two weeks after his “homegoing.”

Mary says she’s in “survival mode” … forcing herself to only think about Robert briefly — and not allowing her grief to consume her.

Angie Katsanevas also makes an appearance in the clip … saying she’s missed Mary because she’s not trying to overwhelm her during that time. The two then talk about Robert.

We broke the story … Robert died in Utah back in February, a few weeks after he was charged with felony domestic violence.

Dispatch audio revealed Narcan — a nasal spray that counteracts the effects of an opioid overdose — was administered to Robert before his death.