I often care about a friend, but he doesn't return my messages like this, and he is neither too cold nor too hot for me. What should I do?

If he doesn't reply to you, you don't have to ask him. He may have gone to other things or gone on a business trip, and he won't be able to return your message for a while, so you should choose to wait until he returns to you. If he doesn't reply, you don't have to bother him anymore. Sometimes when he contacts you actively, you can reply to him actively, which is better and saves him trouble. Do what you have to do and don't want to contact him again.