I keep asking myself why it's so d-mn hard for me when I see a woman pass by in the street. I feel like crying every time I pass a decent looking woman, that's how painful it is for me to look away and just let go of it.
If you try to move on but can't seem to, and if you really want to let go of her image and of your 'gimmies', then instead of using her, immediately start praying for her health, safety, and protection from mistakes, lies, lack of true relationship with Hashem and with the important people in her life; from horrible tza'ar gidul bonim, hatred, mental illness, addiction, and early death, c"v.
Then move on with real life and enjoy what you have. If that is hard, then write down gratitude lists in shorthand quickly and about many areas of your life, health, whatever. It will remind you what life is about and what you've got. That's always more important that what you haven't got (fantasy). The fantasy leads only to pain.