hm. You've been dating since January and haven't had "the talk" yet? Try to think of it this way:
If it was HIS brother's wedding and even though you hadn't had "the talk" he took someone else as his date, how would you feel? It's really about people's feelings. Yours included. If you don't want it to be more serious, then it shouldn't be. but be honest with the guy too. he sees it as more serious than you do, it seems.
I believe only news and research that validates my opinion. Everything else is conspiracy and lies.