What do you mean it's hard to miss someone, but my heart is cold?

This sentence means that if you want to solve the pain of lovesickness, only those who miss you can solve it.

In other words, only those who miss themselves can solve the pain of inner thoughts, and those who tie the bell are needed to solve the problem. Reflects a person's desire for feelings and inner helplessness. In fact, feelings can't be satisfied. Don't force any feelings. Just let nature take its course, don't be hard on yourself. Only in this way can you make yourself happy.