Thank you for your question. Some times in life we go back to things that are in our past. There could be something that happens in life that triggers you to begin to think of the past.
Some times people think about what might have been or often think back to how much their lives have changed.
What you need to do is figure out what triggered you to think about a relationship you had 20 years ago.
Some times certain things remind people it could be something as simple as a place or even a food that you both ate tougher. Things tend to jog people's memories.
An example of this is you might drive by a restaurant that you once ate at and you think back to the time that you went there, this is why places and things remind people of things they experienced in their life.
After 20 years and now you are thinking about this and getting anxiety there must be something that never got solved that you needed to resolve. I want you to think about what you are thinking about when this person came to your mind and why you feel you are thinking of this person.
What I want you to do is write down on a piece of paper your emotions towards this issue. Really think about how you once felt 20 years ago in this relationship. I feel the reason why you can not get this person out of your mind is something is lingering in your mind.
You need to write down how you feel so that you can get your emotions out on this subject. I feel if you write it all down you can put all this behind you and stop thinking about this person.
Understanding your emotions is key in discovering why you are thinking of this person.
You want to write down when you started thinking of this person, then you want to think about why you are thinking of tho person.
You then want think about why the relationship ended 20 years ago.
The reason for writing things down is because you have to get all your emotions out.
It is just like if you talk to someone about how you feel, you tend to feel better because once they are spoken out loud or written things become clear.
I feel that the solution will be clear when you talk about it if write it down.
You need to process your thoughts in order to move forward.
Thank you again for your question.