Koi bito (that's right, it is actually two words): Koi= romantic love; bito= person (slang for hito). Koibito, written in katakana or hiragana can have various definitions, such as "sweetheart", "lover", or "boyfriend/girlfriend" (its meaning can be confusing when written this way). However, koi bito written in kanji (as it is in Reunion Files), is simply "the person who loves" and offers no answers on whether or not this person's feelings are returned. In other words, Tifa embodies the traits of "a person who loves", and nothing more. It says nothing about any type of reciprocated feelings from anyone. Resha also stated that, if Cloud and Tifa were in a romantic relationship, Tifa would more than likely be called aikoi or aikou.
When kanji is used, the meaning is "the one who does the loving", but it is unknown if that person's love is returned.
If it's written in kanji then you'll really get koi bito as 'the one who loves'/ or the love is one sided because that's how we actually use it."
While koi bito in kanji has been known to be used for the word "sweetheart", it is extremely rare. Native Japanese inhabitants just do not use koi bito written in kanji for the word "sweetheart", only non-Japanese and/or die-hard anime/manga fans. Koi bito= lover, as in "someone who loves", not "_____'s lover". It isn't used to imply reciprocated feelings (unless, perhaps, it is written in either katakana or hiragana).
In other words, regardless of what your generic English<--->Japanese dictionary says, the true definition of koi bito is not "sweetheart". So, all of you rejects running around pasting images from your dictionaries can stop now-- all you are doing is displaying your ignorance to everyone. Resha, Saicho, Kenji, and Shadow Spirit have already politely asked that you stop mangling a language you don't understand. I think it is time that you do so and stop basing all of you so-called "proof" on one word that is merely there as a descriptive. Frankly, it is rather pathetic. Is all you have really that one word???