I'm seeking an advice

What a difficult spot for you to be in. But call it for what it is. This relationship has no potential whatsoever. I do not mean to be cold about this. You both have deceived yourselves. You have made the assumption that what you have is actually important. The sexting has given the 2 of you an emotional connection based on infatuation and novelty in the relationship. How is it actually possible that within 4 hours of a conversation that you can know you are serious? It is not possible.
She says she will never trust anyone if it turns out you were playing with her like others. Please do not believe this. She will be hurt. But this has happened to her before. We all have resilience. We all get past difficult times in our lives. She will recover. Maybe she will realize it is best that she works on real life relationships and not sexting and that would be good for her.
You have 2 options.
1. Offer to be friendly with her but no sexting. I think this is a difficult choice. It is too easy to get back to the sexting.
2. Be honest. Tell her that sexting is affecting your life in a negative fashion. That you know in your heart that this relationship cannot really go anywhere but that you had fantasies of it doing so. Apologize. Then end it.
I hope I have not come across as cold.