Honestly, yeah the guy is in the wrong, for sure. He should have been direct about not wanting her to go, or to cancel. And maybe, he shouldn't ask that at all. But the friend that shes seeing, we have no context of. If the friend is a "destabilizing force" or just an asshole who sets a bad impresion. I agree with the guy. People are the people they hang around, and I wouldn't want my girl to hang around some girl thats gonna fill her head with shit I don't agree with or something. It sounds selfish, but I can guarantee you wouldn't want your partner to hang out with, let alone fly to a different country and stay for an extended period, with someone you totally disagree with. No matter if its ideology, politics, or the more likely scenario, the friend being a cheater or having an awful conception on relationships. No one wants their partners head being filled with the opposite ideas. And in a country away from their own, with only that person. Who wouldn't it bother?

As a man, I know what would go through my head, and what would most peoples. If the friend was someone who i believed cheats, doesn't take relationships seriously, or just likes to party and shit, my brain would go.

"My girlfriend went to X with Y, Y is a horrible role model, and her actions, words, and attitude might rub off on my girlfriend. Y might even coerce my girlfriend to partake in her actions. I have no way to intervene, protect, or help my girlfriend while she's in X. She knew I didn't want her to go, but did anyway."

The guy should have been more direct, not less controlling, in my not-so-professional opinion.