Redpepper, here is how I would feel as the mono in such a situation as you are facing. Note I am NOT trying to say this is how (your) mono thinks and feels; but it is definitely how I would think and feel.
Please bear with my possibly childish analogy; you will see where it is going.
Long ago, I meet my wife. She gives me her unique flower. She says: "Look after this flower ; it is unique and special. I am giving it to you because you are special."
So I cherish the flower.
Much later, she tells me that she wants to give the flower to someone else too. I am sad at first, because I think that maybe I am no longer good enough for her to hold her flower; but I try and I do see that actually it is beautiful that she wants to share her flower with someone else too.
I see that truly nothing has been lost.
But then she tells me that she wants to give her special flower to another, and then another; in fact she tells me that there is possibly no limit to the number of people she might want to give her special flower to.
So I begin to not want her flower.
It is NOT because I feel that I am not good enough; it is no longer about me. I am strong in myself and know that I am fine, there is nothing wrong with me.
It is just that I can see that her flower is no longer very special at all, because she wants to give it to so many people. It is not worth very much.
I will still love her as a friend, but I don't want her flower.