This is how Korean quotes a thought or an offhand remark. The remark ends in the soft 는데 ending, which trails off rather than finishing, and then 이러다 stands in for saying or doing that. It maps almost exactly onto the English and you are like, followed by the line: I hope it gets cancelled, I have not worn that in ages, I really must not get this wrong. Most of these lines use it with the while form, describing what someone was muttering as they did something else.