Monogamy is the practice of having only one romantic partner. Stricter interpretations of monogamy mean abstaining from sex until marriage, then marrying and staying with one person for life. Until recently, this was the Christian ideal, and is still the officially endorsed norm of the Catholic Church, which views remarriage after divorce as a sin. Over the past century, however, popular conceptions of monogamy have become broadened across the West. Now, most people no longer expect relationships to last for a lifetime. Instead, they interpret monogamy to mean having only one partner at a time. This is also known as "serial monogamy".

In many cultures, monogamy is not the norm, and peoples around the world have diverse approaches to coupling and fidelity. For example, under Islam, men may marry up to four women and both men and women may divorce and remarry. Across much of Africa, polygamy (one man with multiple wives) is the norm. In other cultures, polyandry (one woman with multiple husbands) is an accepted practice. Polyamory, by contrast, is the practice of openly having multiple romantic partners at the same time, with the consent of everyone involved.

Whatever the relationship style, when someone violates the terms of their partnership it's called infidelity or cheating.

This applies to every sexual orientation. Bi people are no exception. Because of bi erasure (society's tendency to erase bisexuality by consistently assuming it doesn't exist) society only really acknowledges bi people when they are polyamorous and have partners of more than one gender. With it so obviously on display, the existence of bisexuality becomes much more difficult to deny or dismiss. As a result, there is a stereotype that all bi people need multiple partners or that they will invariably cheat. That isn't the case. Instead, the reality is that society routinely assumes bi people are gay or straight when they're really just monogamous.