You are sinful for not sending the nafaqah of your son. You don’t have to divorce her as she is the one who left. You can wait until she files for khul’a.

My wife went to her parents home saying she will return back after 3 to 7 days, But she did not return. Its almost 9 months now. My son is only 1 year 2 months now. I did not send her any money during this time. Now I think, she will not return.  I know that I don’t have to pay her Nafaqa, as I asked her not to leave and inquired when is she returning, she said she would return but it turns out to be lie everytime. I would like to know should I wait until she ask Khul from me to send my sons Nafaqa. Am I zalim if I am not paying my sons nafaqa until now.  Note : Divorce had not happen until now.