my guess is that ra-im was abandoned by her mother, their music teacher, as a child to go be w eunhyeoks dad and thats why eunhyeok promised to be her oppa.
Haesoo thought he is substitute of his mother and now Cha is sick of him so he wants to pretend being his mom but next chp Cha will clear up misunderstanding and they will come back on sex track...
the physical sigh of disappointment i had when he picked up that coke oml
thought he was gonna join them and actually got excited for a bit should've known
i had to pause and take a break, disappointed but not surprised