I have two sons, but the fortune teller said there was only one son in the middle.

So from what you said, only one son can die? It has two meanings. 1 That is, one of your sons will definitely go to live in other places and will not be around you. Then it can only be another son. Another meaning is to tell you that something may happen to one of your sons. Will leave before you. I think this sentence actually means these two things.