Ami-gratus , from the Latin Ami, meaning Friend and Gratus meaning Attractive.
Noun - Attractive friend.
This word is used to describe friends who have a sexual or romantic attraction to each other but aren't seeking to fulfill or even acknowledging that attraction. Commonly used to explain a man and woman who are friendly with each other but the sexual possibilities between them make the term "Friend" inappropriate.

Briefly, "the realization that each random passerby is living a life as vivid and complex as your own." Originally from the Dictionary of Obscure Sorrows, which has a lot more beautiful neologism definitions like this you might enjoy.