When Ren didn't turn up for quite some time and Fang realised that they'd be late if they delayed any further, he called Ren on his mobile phone.
Ren didn't answer the call. Which was something that almost never happened. No matter how angry Ren was with Fang, he would always receive Fang's call – and Fang did the same for Ren. After all, even if they were angry with each other, that didn't mean that they stopped caring for each other, did it? This was something both of them had agreed on, and unless there were unavoidable circumstances, Ren and Fang would never ignore the other's phone call.
And thus, Ren not picking up Fang's call just after they had a disagreement – this was something that made Fang very anxious. For some reason, his chest felt rather stuffy at the moment, and a sense of foreboding welled up within him.