Sassy,
There is the painfulness in grieving, that is enough! Then you beat yourself up for your feelings! As though there is some lack in you that causes them to arise! We all grieve when we experience loss, self help books or not.
Once a well respected Buddhist teacher received a phone call that his mother had passed away. One of his students asked if that disturbed his peace. His answer was “of course I’m suffering, she was my mother!” We can’t run or hide from grief, and it only adds another layer when we self criticize.
For the fantasy, perhaps you could make space around it. Let the fantasy be there. Try not to chase it down, but notice it there, notice the pain there. “Wow, this vision of him with a woman is painful, vibrating in my head and heart.” Then wish him well. “May he find joy, peace and love.” It may be through gritted teeth at first, but keep at it. If you can steer into the pain in such a way, the attachment to him will weaken, and eventually the fantasy will have warmth instead of pain.
With warmth,
Matt