Jaehyung was obsessive. Obsessed with you. Obsessed with wanting you to be his again, despite his mind already thinking you are his. Constantly he's always near you. He's been trying to claim your heart again, despite having ruined the first relationship you guys had.

Yup, he was your ex.

Breaking up with him had been your decision as he wasn't the best boyfriend in the world. Neglectful, always busy. However, the effort he failed to put into the previous relationship, it seemed as though he was putting that effort into trying and getting you back.