I too agree that Sam shouldn't have told Amber about what he and Brett did with Ryan and Caleb, and that it's not her business to be prying about it.
The thing is...I blame Sam squarely for Amber's bad reactions here, because she never would have had even an inkling to pry about what they did, if he hadn't gone and opened his big fat mouth about it. What he does is his business - until he goes and blabs about it, thereby opening up the proverbial Pandora's Box and making it more peoples' business than his own.