I think you should ask to move your thread back to newcomers and you will get more responses.
It can take a really long time for resentment to subside, especially when you remain in contact with one another.
Right now you are in a tough spot because you are clearly plan B right now. Luckily for you dating at middle age is a nightmare for most women.
Right now you can ride it out and see if she gives up on dating and gives you another chance or you can push the envelope and in a loving way you can basically tell her she is either in or out. If you have that conversation and she says she out you have to walk and never look back.
Either way you need to be less available. She needs to feel that she may lose you. Until that happens she is just going to keep doing her own thing until eventually she meets a decent guy.
If you have truly changed and you know your value you will not wait around forever so the clock is ticking and you need to figure out what you are going to do moving forward.