Referring (just for the heck of it) to the original question: Would you put your partner in your will? (Not married)
No. I had various partners / GFs / SOs over the years before getting married, and I never put them in a will. At the same time, I never had a will (just account beneficiaries). They were never my beneficiaries, though -- I had my parents and siblings.
Re: the language, it is definitely cultural. I'm American, 44, and would still probably use girlfriend if I were in a committed non-married situation of any duration, many due to the lack of other options. However, we recently moved to Canada, and folks here use partner A LOT, for all circumstances (same sex / not same sex / married / not married) and it's kind of great. At the same time, the American in my tends to assume same sex when I first hear it. I'm slow to adopt new language / accents, so I imagine it will be a while before I pick it up but I am definitely pro-non-gendered and non-marital-status-specific language whenever possible.