You don't want to lose that image. Let it burn in so you'll remember it always. Next, try to figure out what clues you missed that allowed you to get tangled up with someone who would do that to you. Try to fix you so it doesn't happen again.
Keep the wound clean and dry and covered to promote healing. Take ibuprofen for pain.
The image will fade over time, you can't speed up the process. Like the above statement, keep your mind clean (don't talk to her or see her at all), take Ibuprofen for pain (go out and meet new people).
And also don't carry this into your next relationship. Learn for your own benefits (being aware of the true status of your relationship etc.) but whatever you do, be very mindful of this becoming an insecurity in future relationships.