Monogamous

Monogamy or Monoamory is the act of being in or desiring an exclusive relationship between exactly two people. Neither of the participants in a monogamous relationship are part of a relationship with more than two open and it is not an open relationship. The term monogamous is commonly used by polyamorous people to describe relationships with only two people.

Monogamy vs. Monoamory
Under the most strict definition of the term, monogamy refers to marrying a single person at a time, while monoamory refers to being in a relationship with only one person at a time. However, the term monogamy has come to be used as in a more broad sense and can be used regardless of whether the people involved are married.

Resources

 * 1) https://pride-flags-for-cishets.tumblr.com/post/149195445851/monogamy-pride-flags