고 쌓이다

pile up and up

쌓이다 is stuff accumulating by itself, and repeating it as 쌓이고 쌓이다 stresses how long the build-up went on. Every line here is that doubled form, and most are about feelings and stress accumulating until something gives: 그 스트레스가 쌓이고 쌓이면, 쌓이고 쌓이다가 이제 터지는 거잖아요, 쌓이고 쌓이고 쌓이죠 감정이. It works for time as well: [가족과 함께한 시간이 쌓이면서] 그 시간이 쌓이고 쌓이다 보면. 쌓다 is you stacking something up; 쌓이다 is it piling up on its own.

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