Rowoon wanted to put hat on the head but Wonyoung hit him and he stopped

So controlling and toxic behaviour

I can't see it probably but was the hat green?

there's a saying in chinese about wearing green hats

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In China “wearing a green hat” (戴绿帽子 or dài lǜ mào zǐ) is an expression that Chinese use when a woman cheats on her husband or boyfriend because the phrase sounds similar to the word for cuckold. This apparently dates back to the Yuan dynasty when the relatives of prostitutes were forced to wear green hats.