The Oct. 3 incident was defused with the arrest of Colvin, 35, at the home he shared with the victim and her children on the 16800 block of Lappans Road.
He also was charged with false imprisonment, reckless endangerment and hindering police officers. Those charges were dropped in exchange for the plea.
The incident began at 11 p.m. when police got a call of a domestic dispute in progress.
When troopers arrived, they heard Colvin's 34-year-old girlfriend screaming and glass breaking and soon saw her trying to get out through the broken glass in a door.
Deputy State's Attorney Charles Strong said troopers saw blood on the woman's hands and face as she ran toward them.
The woman told police that Colvin pointed a gun at her and refused to let her and her children leave, police said.
Queried about the gun Thursday, the woman said she couldn't remember if there was a gun that night.
Initial negotiations between Colvin and police resulted in the release of the 7-year-old boy and 13-year-old girl around midnight, police said.
Once everyone was out of the house but Colvin, police surrounded the house and waited, believing that he was armed, police said.
The state police Special Tactical Assault Team Element negotiated with Colvin, who came to a rear door at 2:45 a.m. and was taken into custody without incident.
"He does have a handgun and it was there," said defense attorney Lewis Metzner. "But it was packaged away safely."
Metzner asked for probation for Colvin, saying the incident was a mutual fray. He said that the children were no longer living in the home.