Texting a girl that clearly has a Boyfriend but still flirts with me.

Hey, im 20y and have a problem and i dont know what to do. Theres a Girl from vocational school that is very touchy and flirty when im around her and we get along very good. I know she is in a relationship thats not going too well. Im not very experienced in terms of dating stuff and relationships to be honest and i really dont know how to behave.

Im texting her everyday and she keeps flirting and keeps writing first. At first i didnt think much about it but now its making me a little bit uncomfortable that she has a boyfriend that doesnt know anything about this. We never kissed or met for a Date but it still feels very intimate to talk or Snap with her. Sorry for bad wording btw. English is not my first Language. Im scared that if i tell her that im uncomfortable about the situation might destroy everything, but on the other hand i feel bad for her boyfriend and dont wanna be used as a tool by her to relieve some stress. I would never meet her behind her boyfriends back or something i just like her and dont really know what to do. She told me that her boyfriend and her always fight and it doesnt really feel like a relationship anymore.

What should i do in this Situation? Thanks in advance. :D