Marriage or not?

I really don't understand all this fuss about gay marriage and civil partnerships. It seems to me we're getting completely lost in terminology here and that's what the real issue is about. If we forget the words "marriage" and "civil partnership" for a second and just say we have 2 terms "A" and "B", then I believe the following is really what the whole argument is about

If "A" represents the view of religion - that 2 people are considered to have a relationship in the eyes of any/every relevant god

And if "B" has nothing to do with "A" but rather represents the legal document in eyes of government which says you are responsible for receiving whatever benefits and paying whatever taxes in return if you are prepared to sign that you are in a relationship

Then why on earth are we mixing up "A" and "B" in the first place? Two people of the same sex can sign a legal document to buy a house (and therefore share the responsibility of paying off the mortgage) and nobody bats an eyelid at that.

People are getting lost in the terminology and seem to want to use the same word(s) for both "A" and "B", yet these things are clearly different. One, both, or neither could apply to any individual.

Words change definition over time - surely all we need to do is agree on a definition of the word we use for "A" and the word we use for "B". Or at worst invent new ones for both. Then maybe we can all get some clarity about what the current debates being raged in the names of "civil partnerships" and "marriage" are really about.