“The show is over, as we yankees say,” Sanford writes Charles, “and the girl is my own.” Sanford tells Charles that he had gone to visit Eliza and that the Reverend Boyer had interrupted their talk. Boyer gave them “a pretty harsh look and retired without speaking a word.” Eliza ran after Boyer, but he quickly exited and left town. Eliza told Sanford that Boyer’s “resentment at her meeting [Sanford] in the garden was so great, that he bid her a final adieu.”
When Sanford says the “the girl is [his] own,” what he means is that the girl isn’t someone else’s. Eliza hasn’t consented to a relationship with Sanford, but then again this isn’t what he is looking for. He simply doesn’t want Eliza to be with any other man, and since it appears that Boyer has left the picture, Sanford has indeed succeeded in his plan.
Sanford reassured Eliza that her displeasure and “embarrassments” wouldn’t last, and by the time Sanford returned from his trip to the South, she would be back to her old vivacious self. Sanford tells Charles that his trip southward is “occasioned by the prospect of making a speculation, by which [he] hopes to mend [his] affairs.”
Sanford is leaving town for no other reason than to go see about obtaining a rich wife. This again cements Sanford as a despicable person—he sabotages Eliza’s future marriage while simultaneously securing one (with a different woman, of course) for himself.