More PoliticallyCorrect term than SignificantOther (which could apply to a trained assistant dog).

''I'm not so sure that LifePartner isn't just as descriptive of a dog''

Not to mention that SignificantOther applies to non-permanent relationships, too.

''More politically correct, and even more limply milquetoast.''

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When I hear the term "Life Partner", it always brings to mind this joke:
''We're partners for life. Instead of a divorce, I'm just going to kill you''