Chris was a lazy artist coasting on the income of his nurse, girlfriend.
She was tired of his worthlessness and confronting him about it. They got in an argument–mostly one sided–mostly her. She had a temper. But, it ended in make-up sex.
Afterwords, Mikki was excited because during the sex he had choked her briefly. She wanted more. So, they tried it out. He choked her pretty hard, but she still wanted more.
But this time, he pulled as tight as he could on the garrote. He was fed up with her constantly berating him and saw a solution to both their problems.