and called mouse = new MouseMapper(buffer); in gameLoop(); i....Not a good idea...just poll the mouse-instance for the mouse coordinates. As mentioned, there's the "advanced example". It does the fps-like mouse movement you are looking for. Just have a look on how it's done there.
If you don't want/need that, do it directly on the camera instead. What you basically have to do, is to get the delta-values in x/y direction from the mouse (the mapper does this for you) and rotate accordingly. It's really quite simple.
private void move() {
Matrix rot=world.getCamera().getBack();
int dx=mouse.getDeltaX();
int dy=mouse.getDeltaY();
float ts=0.2f;
float tsy=ts;
if (dx!=0) {
ts=Math.abs(dx)/-500f;
}
if (dy!=0) {
tsy=Math.abs(dy)/500f;
}
if (dx<0) {
rot.rotateAxis(rot.getYAxis(), ts);
}
if (dx>0) {
rot.rotateAxis(rot.getYAxis(), -ts);
}
if (dy>0&&xAngle<Math.PI/4.2) {
rot.rotateX(tsy);
xAngle+=tsy;
}
if (dy<0&&xAngle>-Math.PI/4.2) {
rot.rotateX(-tsy);
xAngle-=tsy;
}
}