She has a bf but we still like each other, what should I do?

Ok so there's this girl, we meet last year and been talking/texting for about 3-4 months now. She has a bf and it isn't going good but she still can't leave the relationship because she loves him. I know because she tells me everything pretty much. We always flirt and these last couple weeks been hanging out a lot at school during lunch just whenever. We text everyday. I hooked up with another girl and she found out about it, at first she was making a joke but I would later find out she was somewhat kind of mad even tho she has a bf. It was good she found out because after we expressed our feelings I told her I like her and how I thought of her as a person. Then she said she feels things about me and I she likes me but she doesn't know anymore since she found out I hooked up. Which doesn't make sense she should have told me sooner. I thought ok, our feelings are known but she doesn't want anything anymore since I hookup. And she jokingly said I cheated on her and I told her well you have your bf I can't wait forever and she tells me but still they don't do anything besides kiss but barely that anymore and that I still cheated on her. I want her and the way she talks about her bf and how she feels things for me, and how jealous she is if I talk to other girls, I think she might want the same thing. But I don't want their breakup to be my fault... Especially they been fighting and I asked when did it all start and she says since she meet me. So I already feel like I messed it up already I don't want to be the reason for the breakup too. Should I leave her alone? Or just go with the flow and see what happens? Or just tell her I want her?
She has a bf but we still like each other, what should I do?
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