I think my girlfriend is having a "tiff" with her ex-boyfriend?

So today I said goodbye to my girlfriend who was just getting on the bus. Her ex was 'convienately' on the bus as well. She tells me that she hates him and has nothing to do with him. As the bus left, I saw her talking to him and twirling her hair. I'm extremely worried and I don't know if I should ask her or not. I already asked her who it was, but I'm afraid she still might be attracted to him. Any help is appreciated.