People who have been kind to you suddenly ignore you, don't return messages, don't answer the phone? Do not delete friends? How do you explain this?

It may be that he has encountered difficulties in his career or other things, and it is difficult to ease his mood for the time being. Or maybe you inadvertently left him alone. In either case, you should comfort him. The message should be sent with quality and conciseness, so that he can feel your meaning and will reply naturally.