I would think that since Sam's brother got Sam and Pete together, that her brother told Pete that she was in some kind of secret operation where she worked. So Pete should have known before hand that what she did was none of his business. And, also, being a cop meant that Pete himself was sworn to secrecy about some of the work he did, and doing a background check on her was waaaay out of line. I really do wish there had been some fallout from what he did and that he got in big trouble over it.