I remember asking a similar question when I first started visiting the boards a couple of years ago, as myself and DBF were heading there and whilst there we'd be having our two year 'anniversary' and asked what people would think if we got buttons - and boy was I shot down on here

I even got PM's saying that I should leave the buttons for the people who are married and then it doesn't take away the 'specialness' for them!!
I never asked since, but I'm glad many people's opionions have changed. I think people should be allowed to celebrate whatever they like. Some people may never get married, so hense, their anniversary may always be the one were they got together.
Go celebrate - enjoy yourselves!