I could've prevented a stray kitten from accidentally getting stepped on

Me and my friend liked to save stray kittens without mothers and take care of them at her place.

She once brought a cute little grey kitten to her house and we took care of her, fed her and played with her.

My friend's brother entered the room one day (my friend wasnt there) to place a plant in the room, the kitten was playing on the floor with some stuff.

Now her brother was walking backwards (means he didnt see what was behind him) and I could've said "dude, slow down//stop!!!" But I dont know what was wrong with me. I felt like I was completely numb at that moment.

He stepped on the little kitten and she was crying in pain. I felt so bad and acted like I havent seen anything.

To this day my friend always keeps saying how stupid her brother can be without knowing I could've prevented all this.

(The kitten didn't die but she was hurt really badly but she recovered from it)

(I was 13 at that time, I knew what I did. Yes, I regret it. I'm fucking awful.)