A dream about an ex is seldom a message about that person. It is more often a dream about a position you once occupied, or a way of being wanted that you no longer have, or a question you have not finished answering. The figure is vivid because the memory is vivid. That does not make the figure the subject.
Freud thought the ex was rarely the point
In The Interpretation of Dreams (1900), Freud's argument was that the dream you remember is a compromise. The manifest content, the version you can describe over breakfast, has been worked over by the mind until it is tolerable. The latent content underneath is what the dream was actually about, and it rarely looks like the surface.
An ex appearing in a dream, on this account, is a good example of displacement. The feeling attached to the figure is real. The figure is a stand-in. You may be dreaming about being known in a particular way, or about a version of yourself that existed in that relationship, or about an unfinished argument that has since attached itself to whatever is currently frustrating you. Freud's method is interpretive and backward-looking. It does not tell you anything about what will happen. It asks what the figure is standing in for.
This is where the pop-culture version of Freud has done damage. He did not hold that every figure in a dream is secretly about sex, and he did not hold that an ex in a dream means you should contact them. He held that the mind disguises what it cannot say directly, and that the work of interpretation is undoing the disguise.
Artemidorus would have asked what you were doing with them
Artemidorus of Daldis, writing in Greek in the second century CE, compiled the Oneirocritica, the most complete dream manual to survive from antiquity. His approach was empirical and situational. He was not interested in a symbol in isolation. He was interested in the dreamer.
The same dream, he insisted, means different things to a sailor and to a magistrate. A dream of an ex would have sent him straight to questions about the dreamer's circumstances. Were you married? Were you in the middle of a dispute? Was the ex dead, or absent, or present in the dream? Artemidorus distinguished oneiros, a dream bearing meaning about what is to come, from enhypnion, a dream that merely reflects the dreamer's present state, such as dreaming of food when hungry. A great many dreams about exes would have landed in the second category for him. Not prophecy. Residue.
His point was not that the dream predicts a reunion or a return. His point was that you cannot read the symbol without reading the life it landed in.
The ta'bir tradition is careful where others are confident
The tradition associated with Ibn Sirin, the Basran jurist and traditionist who died in 728 CE, treats dream interpretation as ta'bir: an act of analogy, not a claim to knowledge of the unseen. Interpretation, in this tradition, is conditional. It is offered with the awareness that the interpreter may be wrong and that the dream's meaning belongs to God.
Many works circulating under Ibn Sirin's name were compiled long after his death. Where that matters, it is more honest to say "the tradition associated with Ibn Sirin" than to attribute a specific reading to the man. What the tradition does consistently is refuse certainty. It also refuses the idea that a dream figure is simply a cipher. A dream of a former spouse or a former beloved raises questions about loyalty, about what has been left unfinished, and about what the dreamer intends to do on waking. The moral attention is on the dreamer's conduct, not on the absent person.
A dream about someone you no longer see is not a summons from them. It is a visit from the part of your life they occupied.
Where the three readings actually disagree
Freud reads the ex as a substitution. Artemidorus reads the ex as a situation to be assessed. The ta'bir tradition reads the ex as a prompt to examine your own conduct. These are not three ways of saying the same thing.
They disagree most sharply on what the dream is for. Freud's dream is a disguised wish, working backward. Artemidorus' dream is a piece of information about the dreamer's circumstances, sometimes about what is coming. The ta'bir tradition places the dream within a moral and religious frame where interpretation is analogy and certainty is not available.
They also disagree on how much the figure matters. For Freud, the ex is often a decoy. For Artemidorus, the ex is a fact about the dreamer's history and must be weighed. For the tradition of Ibn Sirin, the ex is a presence that asks something of you.
What to do with the one you woke up with
If you woke up this morning having dreamed about someone you have not thought about in years, the first useful question is not what the dream means. It is what you were doing in it.
Were you trying to explain something and not being heard? Were you watching them from a distance? Were you relieved to see them, or uneasy, or indifferent in a way that surprised you? Artemidorus would have started there. So would a careful reader of Freud, who would ask what feeling the figure carried, not what the figure's name was.
The second question is what the dream touched on waking. A dream about an ex often lands during a period of change: a move, a job ending, a friendship shifting, a year that has not gone the way it was supposed to. The figure is available because the feeling is available. That does not make the dream meaningless. It makes it specific.
The third question, and the one the ta'bir tradition would press, is what you intend to do.
None of the three traditions promises that the dream predicts anything about the person you dreamed of. They were not written to flatter the wish that a dream is a message from someone who has moved on. They were written to give the dreamer something to work with.
You have the dream you have. It arrived with a particular face and a particular room and a particular thing you were about to say before you woke up. That is the material. The traditions are tools for looking at it. The dream itself is yours.