falling out of love...

I think that you can say you have already fallen out of love when you don't feel any emotional pain (like sadness, anger, resentment) anymore. For instance, you would usually feel that you wanna cry whenever you see or even remember your ex. If you've already moved on, there is already a feeling of acceptance on your part that it's really over and that there's no going back to each other's arms. You are already happy for the person and would never feel pangs of jealousy whenever you hear that he/she is dating someone else. Lastly, you have also moved on if you have already considered dating someone else for the main reason that you're entertaining a new person, and not for the reason of using that person to forget your ex.