Warning this is a mumsnet style thread.
My cousin is getting married this summer and at their engagement party last year my girlfriend (of 9 years) and I were both invited and given a save the date card.
So... you have both been invited?
Fast forward to today and I have received an invitation to the wedding that is just for me and makes it clear that I can't bring a guest. I double checked and it was the intention to not invite my girlfriend.
No, no you didn't
So as far as you are aware, the last communication you received on the matter is that you were both invited 

