I didn't find "Cecily on the dock without a chaperone" confusing. Her father wrote her off. He said, "You have little value to me now." Remember, he still thinks she slept with GC - and not only was Cecily alone with him before the wedding, but for multiple days with the Poldarks. He has no reason to believe she's a virgin, and for all he knows, she has a word-of-mouth reputation in London now too.
His only revenge is that he will keep them apart - he promises her that if they stay together, he will kill GC. That's what he believes will "get back" at her, to separate them. Otherwise, I don't think he cares what she does anymore. Hence: no chaperone.
But yes - for the first few episodes this season, Cecily was very practical, and even at one point, told GC that she didn't want to get married. I think she fell for him, and saw GC as a way to escape marriage to George. But otherwise, she's perfectly happy being independent. I actually liked the ending to this story. I just wish they would have taken a scene or two to establish Cecily and Kitty as friends so we could feel they were heading out there together.
THANK GOD HORACE IS OK. One more episode. Horace and Garrick both better make it to the end! I don't know how old these dogs are, and I don't care.