Well my assumption that we were both agreed that we're past the dating stage (like I said from the other post) was to do with the fact that we've defined it as a relationship, we've been calling each other boyfriend and girlfriend and he's been telling people (including family) that he's in a relationship.
I had felt that we had established rules but it turns out there's been a lot of miscommunication between us and that is something we have steps to work on. At the time I felt he knew my expectations and had gone against them which is why I was upset but then as I say at the heart of it we know, now at least, that there are serious communication issues.
Regarding what I said about non-monogamy you are entirely right and it's really got me thinking about things.
I feel like there is a difference between existing partners and taking on a new partner so when I said non-monogamy it's not really what I meant. When we got together he was with a partner, B, who I had no issues with whatsoever. I wouldn't ask for monogamy, just not to form anything new until the foundations are set.
I understand that there is an argument against this in that love is a natural thing that you can't control. hopefully when we start discussing things I'll realise that there's an underlying issue that we've not realised and can actually be tackled so I'll get past it, but at the moment I don't see anything wrong in giving time to develop the foundations and trust needed in a new relationship.