What should I do if I feel particularly sad every time I don't hear from him?
That may be good after a long time. You should be mainly not used to it now, and it's not that easy to put one down in your heart. You will be anxious and sad if you don't hear from her at all, and you will be extremely happy if you see some news from him. Personally, I think I can't go on like this. I live in a world that cares about others. You should go out more often for fun. If it is doomed to have no ending, it is better to give up early so as not to suffer.