Why is Jack pissed that Pilot wanted to go to Seattle?

Ok, I get it. He thinks its just about a girl Pilot wants to track down, but why can't he kill two birds with one stone, so to speak. They have to leave town anyway, so what difference does it make where they go? Seattle is as good a place as any, so they get to leave town and Pilot gets to see if he can reconnect with his girl. What's the big deal?

As far as the girl goes, I know Pilot was bummed out that she didn't remember him, but she was whacked out of her mind on drugs. If he really wanted to reconnect with her, he could have gone back to the music shop where she worked and may have been a little more lucid. But instead, it crushed when she didn't remember him and when he realized the moment they shared didn't mean as much to her as it did to him, he probably lost interest