I interpret that as plural, "those who are nearest and dearest to me", rather than singular, "the one who is nearest and dearest to me".

But I suppose I was inaccurate; it's not that I wouldn't use the word "dearest" at all, but that I wouldn't use the expression "my dearest" to refer to my significant other in the third person. (Maybe in the second person, i.e. when addressing them directly, but not when talking about them to others.)