A hot-headed ex-boyfriend used a shotgun to kill his girl’s new boyfriend before committing suicide in a restaurant parking lot on Long Island, according to Suffolk County police.

Jessica Kasten, 28, and her boyfriend, Frank Panebianco, 28, were leaving Long Island Pour House around 11:20 p.m. Sunday when they ran into her ex, Michael Skiadas, and his pal in the parking lot on Patchogue Road in Port Jefferson Station, law enforcement said.

After an argument, Skiadas, who was riled up, went to his car and grabbed his shotgun, cops said. His buddy, Jack Schneider, 32, tried to calm him down, but Skiadas hit him in the head with the gun, cops said.

Kasten and Panebianco tried to get away by driving north on Patchogue Road, but Skiadas caught up with them and ran at their car, firing two rounds into Panebianco’s chest, cops said.

Skiadas went back to his car and fatally shot himself, cops said.

Panebianco later died at Stony Brook University Hospital. Schneider was treated for non-life-threatening injuries and Kasten was unharmed, law enforcement said.