Thank you for your question!
I understand what you are expressing for I have experienced that.
Here is what I found: The harder you try to forget, the harder it will become to forget that person.
The more attention you pay to that, a greater fantasy will be built in your mind with the feelings and emotions which will strengthen that experience of remembering someone who you do not wish to or that you are trying to close your feelings to.
Just open your heart, send good wishes and “move on” in your mind to the next thought. As long as you keep good feelings consciously and you are not building stories in your heart or mind, forgetting will happen; but as we know; it may take sometime. This is a karmic account for the mind to settle.
Conquering is never done through force. It is done by letting go.