Everyone remembers their first kiss, and Ben is no different. When he thinks back to his childhood in Eudora, he can't help but think of bombshell Elizabeth who made out with him behind the Methodist church. The trouble with Ben's fond memories of Elizabeth, though, is that he places too much stock in them—he and Elizabeth are married to other people by the time we catch up with them in the book, which means they have different loyalties.
Elizabeth says it best when she points out:
"I should be riding home with Richard. I should be sharing memories of Mark Twain with him. I should be in love…with Richard." (57.10)
She feels guilty for having a grand old time with Ben instead of with her hubby. Perhaps this is why she goes on to betray Ben, telling her husband his plans. Either way, no matter how thrilled Ben is to reconnect with Elizabeth, in the end she's bad news.