He's furious, he's angry beyond words. He just witnessed the guy you were going out with flirt with a bunch of other girls, not caring whether or not you might see him; and what pissed him off the most was that you loved him too much to think he's the problem, and not you. He tried to act normal when he saw you walking timidly to meet up with that guy, apologizing for something that wasn't even your fault to him all over again.

"Don't tell me you're gonna apologize to that bastard again..."