They may be grouped as synonyms or may be very close in meaning but there is always a nuance and that’s where the whole subtlety lies.In the run, you may end up breaking up or tying the knot with him/her.#5 The chances for unfulfilled romantic feelings are high.
Adding to that, it derives the true nature of a boyfriendship/girlfriendship.
In short, there is a difference between a girlfriend/boyfriend and a fiance(e).
#4 May see each other occasionally, or even a little more.
If you’re not serious with someone, why see them all the time?
Might as well see them on occasion, or maybe regularly, but not most of the time.