If you no longer want to contact a person, you can tell him directly. I think there is no need for the two of us to contact him again.

If you also think this expression is too direct, you can tell him more tactfully that you are afraid that your contact with him will be an interruption to him, so you will not disturb him again in the future. This way he will also know that you don't want to contact him.

In fact, if you don’t want to contact him, another way is to simply not reply to any of his messages. He can know through your behavior that you don’t want to contact him. Under normal circumstances, he will not contact you again