Why can't I move on from this?
Francis you can't move on from it because you are trying to move on from the sad reality that your husband loves this OW. You know he does and you know the affair wouldn't have (still hasn't) ended if you hadn't threatened to tell her husband, boss and mother. The fact is the affair ended by default and not because your husband or the OW wanted it to end.
There's a voice inside of you telling you all of this and the fact you've not been able to silence it shows you know deep down inside that you're sadly living with a man who doesn't love you and is still at least having an emotional affair.
There are two ways for you to live this. You either accept the situation and learn to live within your marriage the way it is with all that it entails. Or you listen to the voice thats telling you that this situation is never going to come right, that no amount of trying to make your husband love you and not her is ever going to work, and you bring your marriage to an end.
Have you had counselling? Have you had the chance to ask someone to help you to understand why its so important to you that this man loves you? What is it about your make up/self esteem that has you hell bent on being the one your husband loves? Is it some kind of competition you have to win? Do you actually want him or is it that you don't want to be the 'loser' in this and for her to have him. Why do you not think you're worth more than this? Is a song worth this?