therefore creating a gap in the center of the wall for grouting... or tiling one tile and grouting it with the gap at the wall and the next tile side putting a grout line down that way
the answer is yes you need that gap.
Tile one wall all the way to the corner, leaving a small gap at the wall to compensate for any wall movement. Then tile the other wall. leaving the same size gap as your grout lines between the two. You do not want to have a void in the corner.
