two people in a romantic relationship
couple
your boyfriend, girlfriend, husban or wife
partner
the person you are engaged to be married to
fiancé, fiancée
a person that you share a flat with
flatmate
a person that you work with
colleague
a person that you used to have a relationship with (colloquial)
ex
a very good friend that you can talk to about anything
close friend or best friend
a friend from school
classmate
