Katsuki had PTSD from various traumatic events. Nobody really knew about this except Kirishima and, well, you. Kirishima knew because he was the closest thing Bakugo had to a 'best friend'. You knew about his PTSD because you had accidentally heard him have a panic attack in the middle of the night once since the dorm walls were so thin.

Having been raised to care and worry about others, you went to check on him. Of course, he denied everything when you stood at his dorm door, but later he opened up about it because you caught another one of his PTSD episodes. You knew Katsuki didn't like talking about himself, especially about his feelings so you just let him be, telling him he could come to you whenever he needed to, even if it were just for some silent company. As his PTSD worsened, he gradually came to your dorm more and more. You two would rarely do anything but sit in silence, doing your own thing until his panic attacks subsided and he would leave.

It's around 1 am when you hear a soft yet firm knock on the door of your dorm room. slowly getting up and opening the door, you see Katsuki in his pj pants and black tank top. his hair was disheveled and his eyes were tired yet wide. You knew why he came so you just stepped away and let him enter. What you did not expect was that he would go and lay down in your bed. It must be a bad PTSD episode if he willingly laid down in your bed.