I haven't been together for four months. Never take the initiative to talk to me when we are together. Today, he sent me a short message. Hello! Busy? How should I reply to his message?

If you still care about him, reply that he is not very busy. Why have you been out of touch for so long, and suddenly you think of me? If you don't care about him, just reply that he can still be separated, so don't contact, it's good for everyone! If you don't reply, you feel you owe him something. It's better to reply.