What's a good term for our relationship status?

My "girlfriend" and I have been dating for 3+ years and living together for 2+ years. It's a committed relationship very much like a marriage but after considering the pros and cons we have chosen by mutual agreement not to get legally married.

We don't particularly like the terms "boyfriend" and "girlfriend" because they seem to us more like something for people in their teens or 20s than people in their 50s and we don't think they convey the depth of relationship that we have that is very much like being married but without that legal status. "Casual relationship" is the same. We're serious, not casual. "Husband and wife" are for legally married people, "fiancée" is for people planning to get married, "significant other" doesn't sound that good to me, and we think a lot of people interpret "partner" to mean a homosexual relationship so we really don't like any of those terms.

We're mostly using boyfriend/girlfriend, sometimes SO, but think there should be a new term for "major committed relationship without the legal status of marriage". Anyone know of an existing term or have good ideas for one?
What's a good term for our relationship status?
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