Some libraries that are c/c++ like allegro that can run on android might be a good option for you. It's either allegro can do it or they are working on it. Either way Idk how it works, but I would check it out. Someone else might know some more libraries that can do the same thing.
It's because you only have it set to update when space is held. From my knowledge you would want to have a state for the bullet being checked to see if it's still alive. If it's still alive update its position, if not remove it. I think that's right.