One thing Seulgi never understood about Joohyun was how confusing and complicated she was. 

She was like an intricate maze you get lost in but could never find your way out of. It could get frustrating at times (Seulgi didn’t want to dwell on the likely possibility that perhaps she wanted to remain in Joohyun’s maze and become tangled up in her complexities. That was a terrifying thought).

—

Or, the classic 'and they were roommates.'