alright this is just one way of doing it....
replace these two lines:
if bdir=2 then move object right 1,0.1
if bdir=4 then move object left 1,0.1
with.....
if bdir=2 then move object right 1,0.1:position camera newxvalue(camera position x(), camera angle y()+90,0.1), camera position y(), newzvalue(camera position z(), camera angle y()+90, 0.1)
if bdir=4 then move object left 1,0.1:position camera newxvalue(camera position x(), camera angle y()-90,0.1), camera position y(), newzvalue(camera position z(), camera angle y()-90, 0.1)
all your doing in that is using newxvalue and newzvalue to work out new coordinates for the camera by putting in the angle (camera angle y()+90), the starting position (camera position x()) and the step value (0.1)