I was thinking about that.... maybe Daryl doesn't tell Carol everything about Negan and what he has done. And that's why Carol doesn't leave with Daryl. We know Daryl will share scenes with Morgan Ezekiel and Richard. So its reasonable to think that maybe they update him on Carol's condition. So when Daryl finally reunites and talks with Carol he realises how fragile Carol is, and decides to hold back on telling her everything .