Can you wear the same dress to two weddings?
Yes - unless the guest lists overlap heavily. Change the layer, shoes, and jewelry and it reads as a different outfit anyway.
Nobody tracks your wardrobe except you. The practical rule: if the two weddings share almost no guests, wear it without a thought. If the overlap is large (same family or friend group), the dress is still fine - vary the register: different shoes, different jewelry, add a blazer or wrap, change the hair. These change the outfit's impression more than the base garment does. The piece people actually remember is the loud or distinctive one: a bold print reappears in photos and registers; a solid midi in a dark tone is essentially invisible to memory. If the repeat still bothers you, this is exactly what rental services exist for - the second wedding's outfit at 10-15% of purchase price, no closet cost afterward.