Gordon didn’t have much self esteem. He’d regularly go out with the guards, get wasted. Sometimes they’d drug his drinks, sometimes he just pretended they did.
He let them do whatever they want with him.
That’s why, some people escaping Black Mesa would occasionally come across a scene of a guard bludgeoned to death with a crowbar. They weren’t killed by HECU bullets, zombie claws or bull squid acid. They will killed by the cold revenge of a man who finally got control of his life, after being a pawn for years.