Relationships

How do you forget someone that keeps lingering in your mind?

It has been going on for years now, I had two children but he's always on my mind. No one had ever had this effect on me and no I cannot block him on social media he would somehow mingle back to my life. We are normal friends that talk once in two months or more just to say hi nothing more. We have never been in a relationship. No matter how many people I met in my life who were interesting, high value or charismatic and I consider myself to have a lot of options, he is like just there for no explainable reason.
How do you forget someone that keeps lingering in your mind?
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