6 months or 1 year & 1/2?

My boyfriend and I made things "official around October 2015, we started out as friends with benefits on September 6th, 2014, and I like to say we've been together since we started being "fwb" because we were faithful to each other, we would hangout all the time, and we wouldn't see other people, the most either of us would ever do is text other people. 
But I just feel like I can't say we've been together since the night it started, he says I can and so does everyone else I talk to it about. 
And it's not like we just met up to have sex, we'd actually hangout a lot. We'd go on walks, hikes, swimming, fishing, and do stuff that couples would do.  
I eventually started staying with him around January 2015 and I'm still staying with him. I don't want to have to say we've only been together for six months but I don't know if I can say we have been together for a year and a half. 
I'm sorry for the rant, this has really been bothering me for a while now and I have finally decided to say something about it.