Partner
From the Simple English Wikipedia, the free encyclopedia that anyone can change
A partner is someone with whom a person shares an activity, i.e. they do something together.
Very often the word partner is used to mean a person with whom one has a sexual relationship. People who live together but are not married may describe themselves as "partners". Partners may also be gay couples.
In dance a partner is someone with whom one dances.
In business a partner is someone with whom one runs a business.
In card games such as bridge partners are two people who are playing together on the same side. They are trying to win from the other two people who are their opponents.
A relationship of partners (in any sense) may be called a partnership.