
Yep it was Dohyun, this is how it was written in the Novel (no spoilers)
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"I missed you."
Wooyeon casually uttered in a light voice. He also playfully packaged it as a joke so that Dohyun wouldn't misunderstand, saying he had various thoughts because he was in pain. Dohyun stayed silent for a while, then replied with that courteous and affectionate tone.
"...I'm glad."
That day, it rained in Wooyeon's heart as well. It was a downpour of cherry blossoms.

here you go, that's the exact chapter where this episode is
https://chrysanthemumgarden.com/novel-tl/at/at-23/
Sometimes I wish the chat bubbles were colored. Who said thank goodness?! (/TДT)/