It could mean a lot of things, or, more likely, it could mean absolutely nothing! Dreams are funny things. Nobody knows exactly why we have them, or what they mean- if anything at all (despite the numerous theories that are banded about).

Many people believe that dreams deal with the
repressed feelings in your unconscious mind. Feelings that we may not be even aware of. In contrast, others think that dreams are just the body's way of processing things that happen during the day, or that are on our minds.
Sometimes these take the form of nonsensical images or events that have happened in our past, and we don't know why, but there is no need to read too much into it.
If you are worried, you should talk to the person you are in a relationship with, but you really have nothing to feel guilty about. Unconscious thoughts are exactly that; unconscious. Beyond our control. I still have dreams about people I had feelings for over 10 years ago! It makes no sense, but neither do any of my other dreams to be quite honest!