You need to mature enough to understand how your boyfriend felt losing his wife and the grief he went through. He loved her and she died. He has finally come to terms with his grief and is moving forward with his life trying to be happy with you. Yes, it is appropriate for him to discuss his late wife as his wife because that is what she is and until either of you decide to get married to each other then you will remain his girlfriend. Think of it this way: He loved her a great deal; she passed away; he was heartbroken, but he chose you and that is quite the compliment so be kind and understanding and not so touchy about him mentioning his wife every so often.
