Why is it so wrong to talk about marriage?

especially when there are kids involved. He has a son and I have a daughter they are both 8. We just had our one year ann. We have looked at rings .. talked about marriage..live together..and now that I have sort of fallen into the mom role with his son..it's a lot more responsibility..I just want the validation that I'm not just the girl friend when i feel like more of a mom.. he says- you are the mom of the house..but it's not enough for me, so when i bring it up- there's an outburst of emotions and conflicting feelings regarding this issue. its so frustrating- why do i have to even bring it up-why cant he just validate his "promise" with a proposal already..