A 20-year-old man gunned down his 18-year-old girlfriend and then killed himself in a tragic murder-suicide in Queens early Wednesday, police sources told The Post.
The couple had gotten into an argument inside the apartment on 84th Street in Jackson Heights just moments before the deadly saga erupted at about 1.50 a.m., according to sources.
A relative inside the home allegedly heard the young lovers fighting before multiple gunshots rang out, the sources said…