Tbh, i think the two switching back is pretty ambiguous. Theres a good amount of arguments both sides, the 64 boyfriend thing isnt as solid as everyone thinks it is, it could also be translated as "youre not honest with your boyfriend". I think they still switched to their switched bodies as yui still acts out going and yuuta is more reserved. I still prefer if they got back into their original bodies as it fits the story better in my eyes, but honestly, just interpret it how you want, not an exact wrong answer here