Answer:
people tend to label who they like and who they dislike. your brain remembers these people who you labeled, "like" and will start to label those people into love, okay, etc. when you see someone who acts like you, looks like you, etc, you gain a sense of comfort. the reason why people are fond of one another isnt much an answer that can be scientifically proven, you have to experience it for yourself to realize why people like each other, either it be in a friendship, romantic relationship, family relationship, etc.
anywho my friend told me this since im really bad at explaining love without the usage of chemicals in your brain, so yeah