I'm still in love with a girl who friend zoned me, even after I told her I stopped having feelings for her. She's currently going after someone else and while I am happy for her, I can't help but feel jealous and heartbroken that I'm not the one she wants. I'm so madly in love with her that even after dating other people, my heart doesn't want anyone other than her
This will be painful but it's in your best interest long term. Confess your feelings to her and include your torturous it is for you to be in this situation. If she doesn't have feelings for you romantically and you can't stop having them for her, then you must end the friendship. It will only hurt both of you in the long-run.