Why didn't Bryon remember Cathy in Chapter 2 of "That Was Then, This is Now"?
Bryon hasn't seen Cathy in a really long time, and both of them have done a lot of growing up since then. Since they have both entered their teen years since the last time they saw each other,their physical appearances would have changed drastically. Cathy comments, "Gosh, you've grown...you must be a foot taller than when I saw you last", so Bryon knows if that's the case, it must have been awhile. When he finally realizes who she is, he tells Cathy, "The last time I saw you you had short hair and braces".
Another reason Bryon can't remember Cathy is because they weren't really close even "back in the days of braces and short hair". Bryon acknowledges he "had never paid any attention to her". When she went away to boarding school, he naturally didn't hear from her, but he kept in contact with her brother M&M, who stayed in the neighborhood. It is because of her resemblance to her brother that Bryon finally remembers who she is.