Her sister got hysterical over her boyfriend who drew a slutty picture of her - how skinny and flat she was. Her brother calmed her down and measured her waist and hip size, assuring her that she was awesome! Sure, her gratitude was inadequate - sucking her brother's cock, but didn't the girl deserve sympathy? When she wanted to remove her head already, he wouldn't let her - if she wanted to be a grown-up, then swallow it. And it seemed his sperm was to her liking. Now she could always count on him.
This young lady got back at her friend in another way! The guy probably wasn't happy to watch that, but he should have thought of that earlier. But when she slept with her boyfriend, her self-esteem probably went up, she got new feelings and ecstasy.