GOOD QUESTION. Many fall in love and before the marriage is over, they fall out of love in divorce courts.
Go back in tradition, when marriages were arranged, and upon marriage, love grew with understanding and tolerance of each other and stood test of time until "death do us apart'.
To fall in love with a person you don't know personally, but have seen before sounds like infatuation. This is a different cup of tea that needs to be tasted a sip at a time, and time will tell if each sip finishes the tea or is left unfinished.