[M X]

It's already been established that Sallie and Dexter knew each other before entering the house, and that hasn't been made a secret of. Sallie and Dexter have both openly spoken about this.

And as far as the supposed 'friendship' between Rylan and Dexter goes, if Dexter's job really is this hugely successful media executive it is likely that he will come into contact with celebrities like Rylan Clark from time to time.