Ok ladies I just needed to ask because I wasn't sure how I felt about this..
FI's cousin is getting married in July (obviously before us lol) and we got our invitation yesterday.  It was addressed to Mr. & Mrs. FI's name!!  
I have addressed this cousin's invite and it is Mr. Grooms name and Miss Bride's Name.  I guess even though both FI's cousin and his fiancee, and FI and I have been together for years, I still thought it should be addressed to them/us separately since neither couple has gotten married yet?  
Our close friends sometimes jokingly call us Mr & Mrs (they say, "oops I forgot you guys aren't married yet since you act like a hubby and wifey already, sorry" lol)..
I just felt a little weird getting the invite since FI and I aren't married.  I was just curious if you ladies would feel weird too or if this is a common thing?  
I'm obviously not going to mention it to FI's cousin or anything, it isn't a huge deal, it just caught me off guard...