He is way in over his head with everything. Kes is much smarter than him and learning at a phenomenal rate. Voyager's crew is a disciplined military organization and he's used to living as a drifter. All the story telling bullshit he's gotten by on just fine is suddenly under scrutiny and he has to cough up something useful for these advanced people on this advanced starship who his advanced girlfriend is seemingly fitting in with rather well. And look at this starship's males with their nice smooth fur-less faces like Kes's own people, why she even looks like one of them..
He's freaking out all over the place.