Tell me about a man who covers for others.

This kind of person is really annoying, but there is no good way. You can tell him clearly that there are two people on duty and you have your responsibilities. What belongs to him can only be helped by your accident. If there is a conflict between two things, you must be responsible for it yourself. Let him figure it out himself.

Anyway, just let him know that it is a mutual affection for you to help him, and it is your duty not to help him. Don't let him think it's right.