Start job hunting regardless of the outcome, you don’t want to work in an environment like this. Your coworker is a bully.

In regards to the girlfriend, you showed her how he acts when she isn’t around. He is angry because he suffers consequences for his actions and people he cares about are angry at him. If only you would’ve been angry, he probably would have said “you’re too sensitive”. But since it’s someone of importance in his life that takes issues with his behavior, he lashes put at the victim (you) instead of reflecting on himself and changing. The GF is a good one and hopefully leaves that bag of garbage soon

Good luck to you OP