Well, I'm not sure what is necessary in life. But shifting your mindset might help your chances of reconciliation.
Imagine you were dating someone new with a very young child. If you don't welcome them as a package deal, even long before you meet the child, the R probably isn't going to go anywhere. If you view them as your beau and that child, your lives won't mesh.
With H, for him, it isn't H and that child. They are now a package deal. If you change how you think of them in your mind, it will show through in your behavior.
Right now, it *seems* as though you see reconciling with H as step (1) and then working that child in as step (2). That is, getting to the point of you+H and then moving to you+H+1. But, there is no longer just H. H simply IS H+1 NOW, and always will be. That IS who he is.
You really seem to be putting up an emotional barrier to embracing that. I don't believe it is simply a matter of word choice between kid and tot. There is emotion and pain behind how you choose to refer to H's DD. You already said that was the case. And frankly, it seems to me plainly obvious AND perfectly understandable.
But this is a place where you can clearly do work on yourself (rather than worrying about predicting/shaping H's and OW's actions). If you can really come to peace and embrace H+1 in your head and in your words and in your actions, you will fare better in your life no matter how things go and improve you chances of reconciliation.
And, to be clear, I don't at all question your ability or willingness to be a loving parent to H's DD.
