What is the reason why Tucker stops talking to Richard

Read the excerpt from the strange case of dr. jekyll and mr. hyde. "my dear utterson,—when this shall fall into your hands, i shall have disappeared, under what circumstances i have not the penetration to foresee, but my instinct and all the circumstances of my nameless situation tell me that the end is sure and must be early. go then, and first read the narrative which lanyon warned me he was to place in your hands; and if you care to hear more, turn to the confession of "your unworthy and unhappy friend, "henry jekyll."