I might have a few things missing, and this is just my opinion, I could be completely wrong here, but..
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Enemy - hope they get hit by a truck, couldn't care less. Forced aggression.
Stranger - obviously a stranger, you don't know they exist, they don't know you exist, but acknowledge each others existences exist. Possible aggression.
Nemesis - Acknowledgement of hate, but don't exactly wish death upon them. Tested aggression.
The "I've seen them", or "I've heard their name" people - You know them, but don't go out of your way to meet them. True Neutral.
Acquaintance - You've met by coincidence, but remain neutral.
Forced friend - People you've met, and are cordial with, but only because you have a mutual friend. Tested neutrality.
Familial - People you're forced to be cordial with because blood ties. Forced interest.
Love interest - Falls under the "I've seen" or "Heard of", or have been introduced to, but only want to know purely because interest. Neutral interest.
Friend - Person you talk to generally about small talk, personal interest, or business with. Tested interest.
Love/ lover - Person you talk to generally about small talk, personal interest, or business with, but also have intimate physical contact with. Neutral Love.
Dating - Person you are trying to get to know well enough to see if compatibility is on the table. Forced Love. (I say forced, because typically people find this person sexy, or interesting, or cute, or fascinating, and want to push forward despite possibly seeing red flags, and despite noticing things they don't like. Testing the waters, but aren't ready to pull back.) Often called blind love.
Partner - Person you are compatible with, and share most, but not all internal feelings with. Love.
Spouse - Person you be comfortable around, and generally talk to about nearly completely anything. Tested Love.
Best Friend - Person you do not hesitate or think twice about talking to about anything anything with casual judgement, and mixed with helpful advice. True, tested, proven, neutral friendship.
Companion/ confidante - Person you don't know, and don't care about, but can ask advice on anything despite judgement. Neutral Friendship.
True Familial - People you choose to familiarize with, and would fight to protect. Tested and proven friendship.
True Spouse - The single most loving person who has seen all your faults, and still loves you despite your stinky bed farts. True, tested, proven, neutral love.
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If seen as a ladder, the reason why someone would backslide into a previous rung in the ladder, would be because it was tested, and it failed.
EX: You Hesitate to call a best friend, when you've never hesitated with them before in your recent life, so they fall back into the regular friend category, either because a fight, a falling out, marriage, life, kids, school, any assortment of reasons. More often than not, it comes down to 2 paths leading forward, call and see if things are still good between you and them & continue with best friend route, or don't call, and solidify the drop to friend status because you questioned their friendship loyalty. It's a deliberate choice, typically made out of fear, or time, and can be fixed or repaired, but the question is.. will it be?
