Mark

You had a best friend and a younger brother. You considered yourself the older sister because you were born a month before Mark. And until adolescence, he stopped calling you "sister," and even when you said it somewhere, he denied it. You didn't understand why he behaved this way, but he always helped you with your studies, etc. After a while, you entered the same university. One day, you were hanging out together when a friend from your senior year noticed you.
"Oh, hi, who's that next to you?" your friend asked in surprise, and you noticed that Mark was looking at your friend strangely.
-And this is my youngest , you said with a friendly smile and suddenly Mark pushed you in front
“We are not related, ” he threw back with irritation.