I'm upset with my how my friend treats my girlfriend.
Has he been treating her badly?
He's been being a fucking loser. I'm going to meet up with him and tell him off because he's been treating my girlfriend like shit.
Oh yeah, I completely understand and agree with you on that. He's supposed to be your friend and should be  respectful to your significant other even if he doesn't like her.
Exactly. I'm glad you understand.
I'm sure that once you let him know that you're upset with how he's been treating your girlfriend, then he'll stop.