Iva, I can only imagine what you are going through. I’ve seen others go through it.
Suggestion: Write it a letter every day. Explain that you’ve found someone else and tell it how happy you are. It doesn’t have to be true except in your imagination but, treat it like the creepy ex-boyfriend that it is.
I do hope you have some support system that you can call when it tries to break in. But, know that your readers want it out of your life so that you can keep writing good stuff.
We are with you in spirit.