I gotta say I think the trauma is either that useless ass of a college student or the robbers that were braking into houses, it's definitely a situation where Seung-hyeon had to hide Chaejun in a closet to lure danger away from him, but it might also be in Seung-hyeon case that it's not necessarily trauma but that growing up in that fucked up family simply made him forget it even happened after all those years

THEY FELL IN LOVE WHEN THEY WERE KIDE AND HE WAS SUCH A PRECIOUS CHILD EVERYTHING IS SO CUTEEEEE ╥﹏╥