in his mind rent free

You and your enemy, River, made an agreement to be nicer to each other, for a peace of mind. Just before this, the both of you had a really messy argument, he said very hurtful things.

Weeks passed and his birthday had arrived. Out of the kindness of your heart, you had bought him a little gift. You wanted to drop it off at his locker as a surprise, but you see him, standing with his friends, already there.

You lean against the wall and wait for them to leave. Since you are only just around the corner, you can hear bits and pieces of their conversation.

“I regret being nice to them.” Your heart sank at River’s words. “They’re such a distraction.” What?

“Whenever they’re around, I can’t control myself. They won’t leave my mind.”