What does it mean when you suddenly dream about a person you don't talk to anymore and had a big fight?

The dream only means that something during recent days brought the memory of that person to your mind - it might have been a place you passed, a bit of music or even a subtle aroma. You need not have been consciously aware of the memory for it to nudge your subconscious mind and trigger the dream. The dream itself may be a message from your own deep mind that it is time to repair the relationship. However, the dream is ONLY about your own thoughts, feelings and memories. It does not mean that the other person was thinking about you.