Anima and Animus
Dreaming of your ex: meaning and interpretation
The bond that left a mark
A past relationship returns. It rarely speaks of getting back together; it speaks of what that story left in you.
Symbolic reading
When an ex appears in a dream, it is almost never a warning about them or an invitation to go back. It is the shape your psyche found to show you something that relationship touched: a wound, a desire, a way of loving or of letting yourself be loved. Notice what they were doing and how you felt beside them: that is what is still being worked through.
Jungian key
Jung would see that figure as a projection of the anima or animus: qualities of your own placed on the other person. When the dream brings them back, it often asks you to reclaim that quality as yours, not the person.
What you look for in that figure already belongs to you. You can take it without going back.