You're gonna love this job. Try this: loosen the PS pump and swap the two belts. Move the inside belt to the outside location. Re-tighten and see if you have the same problem or if it has moved with the belt. If the problem moved with the belt, one belt is longer than the other. If the problem did not move, you have one of three problems. First possibility is that one pulley is worn. This does actually happen. The belts of course actually ride on the sides and sometimes the sides will wear enough that the belt will ride futher into the pulley. Other possibility is that the pulleys are not properly aligned with each other. More to the point probably the PS pump is a bit cocked compared to the other pulleys. Often there will be wear on the pivot bolt or in the bolt hole and that will throw off the alignment. Son had an alternator with severe wear on the pivot and we could not keep belts on it. Had to replace alternator to fix. Third possibility is that the bearings in the water pump are going and allowing the shaft to "bend" in towards the other two. Once again, the alignment will be off. Hint: mark ONE belt with white-out or something so you can remember which is which. It's easy to get confused. Since you seem to have the belt closest to the engine loose, I'm gonna guess that if the belts are the same, you have a worn pulley-probably at the water pump. I think it was the weakest metal.