A 20-year-old man found fatally shot in the stomach outside a NYCHA development in Brooklyn took his own life — but was initially thought to be a murder victim because his gun went missing in the aftermath of the shooting, cops said Thursday.
The 20-year-old victim turned the gun on himself outside the Marlboro Houses on W. 8th St. near Avenue X in Gravesend about 5:30 p.m. Wednesday, cops said.
Medics rushed the victim to NYU Langone Hospital-Brooklyn, where he died, police said…