I have sinned gravely... *Trigger warning*

Hello there my friends. To preface this, I would like to say that I do not know where else to post this so sorry if it is inappropriate for these forums in particular. Also, here is the pmo trigger warning so turn back if you're not into that. So in order to tell of my mistakes, it requires a little bit of backstory.
So, I've been on nofap for a decent amount of time (until recently), and the benifits have been growing ever so steadily. I've been more confident, more focused, and more in tune spiritually and in the word than I ever have been. During this phase I decided to download tinder. This was my first mistake. I matched almost instantly with a girl and we got together and got food. There was an instant connection and I found her very beautiful. We ended up going back to my place and neither of us could resist the temptation and we ended up being intimate with each other to the point where we both finished, although we didn't have full on sex. Basically I felt bad for it but then she came back the next night and we did it again. I felt awful but then she told me she was a high ranking witch in a coven... I am now horrified and do not know what to do. I have been a Christian for a very long time and I do not want these moments of weakness to damage my eternal destiny. I believe in the preservation of the saints, but i cant help but feel like I have gone too far. I would appreciate any and all wise words from you guys in regards to this question of going too far and sinning too great, as it is weighing so heavy on my soul right now.