Yet another plot question (SPOILERS)!
Ok, so when Andrew finds Johnathan in the developing room with all the pictures of Celia he takes them away and says something like, "You disgust me." The audience later discovers that Andrew says this because of Andrew's hatred toward Celia (although at the time we infer that Andrew simply disapproves of his son's voyeuristic...hobbies).
Johnathan is obviously upset by this, but it makes me wonder - at the end when Paul confronts his nephew saying "I know you liked her," was Johanthan upset because he himself knew the dark secret (which I guess would make them cousins?), or was he upset about Celia's disappearance? Did Johnathan ever know the secret and was simply intrigued by Celia or did he have a crush on her in the beginning? Just a little confusing.