I have used "other half," "partner," and "significant other," in conjunction with "girlfriend."
Because The Ex and I were Arrested Development fans, we'd greet each other with "Heyyyyy boyfriend!" a la Buster Bluth.
Even at 35, during the first stages of a committed relationship, I'd use "girlfriend" or "s.o.", but having read through Song of Songs a few times now, I think that after I knew I was in love, and had declared it, I would call her "my beloved."
(It would be weird to call her The Shulamite. ^_^ )