The confidence meter for each pitch is mostly for that game only, although its starting position at the beginning of a game will be higher if you're coming off a good game and lower if you just had a bad game.
The meter goes up if you throw a strike or get an out with that pitch. It goes down if you throw a ball or give up a hit with that pitch. It also goes down slightly over time. Your #1 pitch will drop faster in confidence than your #4 or #5 pitch. That means you need to use your #1 pitch a lot more in order to keep confidence high.