A relationship can represent a real, imagined, or desired relationship in real life.
The relationship person in the dream can actually represent a different relationship person in real life. For example,in a dream where you're back in a relationship with a previous boyfriend, the boyfriend in the dream might actually represent your current boyfriend or a new boyfriend wish you were with.
A relationship can also represent a different kind of relationship in real life. For example, dreaming that you are married to a coworker when you are not likely represents your close day-to-day workplace relationship with that person.