I am a little surprised there are quite a lot of words about friendship. I think there are more, and let me know if I miss any. These are all regularly used words.
buddy:a close friend.
sorority: a women’s student organization formed chiefly for social purposes and having a name consisting of Greek letters.
fraternity: a group of people sharing a common profession or interests.
sisterhood: an association, society, or community of women linked by a common interest, religion, or trade.
brotherhood: 1 : the state of being a brother. 2 : a group of people who are engaged in the same business or have a similar interest. 3 : feelings of friendship, support, and understanding between people.
sidekick: a person’s assistant or close associate, especially one who has less authority than that person.
confidant:a person with whom one shares a secret or private matter, trusting them not to repeat it to others.
pal: a good friend
soul mate: a person ideally suited to another as a close friend or romantic partner.
acquaintance: a person one knows slightly, but who is not a close friend.
bestie: (informal) a person’s best friend.
frenemy: (informal) a person who is or pretends to be a friend but who is also in some ways an enemy
BFF: a person’s best friend.
chum: a close friend
amigo: a friend
beau: a boyfriend or male admirer.
chaperone: a person who accompanies and looks after another person or group of people.
keeper: a person who manages or looks after something or someone.
mate: a fellow member or joint occupant of a specified thing.
bromance: (slang) a close but nonsexual relationship between two men.
squad: a small group engaged in a common effort or occupation.
comrade: a companion who shares one’s activities or is a fellow member of an organization.
flirtationship: (slang) A social situation that comprises more than a friendship, but less than a relationship
superfan: (slang) a person who has an extreme or obsessive admiration for a particular person or thing.