As far as I know, Korean doesn't have very many common terms of endearment compared to the Western languages. 여보 is strictly between married couples. 그대 and 당신 are commonly used in songs and poems for "you", but they are just more literary words. All these terms are more functional (represent "you") than endearing, I think. Another word that might carry an endearing feel is 자기. This term means "oneself", but is also used to mean "you" indirectly, and can sound endearing. Other expressions such as 내 햇빛 are rare except when meant as a joke. I think most people avoid such terms because they can sound corny. Still, I personally don't think Korean speakers feel that Korean is lacking as a language because of this. Feelings are mostly carried in the tone of the voice, not special words, and Korean has a well developed intonation. In writing, the above-mentioned words are common, and when they want more, they'll start to invent their own ways of expressing such feelings.