Just talk to her and tell her you like her in the sense of more than friends and see where the conversation leads. Tell her that you feel she knows that you like her because she's been acting in such a way to make you feel that it's all mutual feelings involved.
I know it's not easy when questioning your sexuality however you can't know for sure until things seem right with the two of you. Also you didn't say if you ever felt that you had feelings for other girls, because that might give you indication. Guys and girls are so different, my personal experience of just getting off with a girl is so different to getting of with a guy, it's something unexplainable but you might think it's best that you do try things before thinking of getting back with a boyfriend you've been with previously because who knows it might feel like being with a girl is right. It's all about feeling comfortable with the person you are with. If you haven't had feelings for other girls it might just be one girl who you feel such a connection with, I've heard it before the some people go out with same sex once and it's because it was only the person they feel in love with, it wasn't about their gender.
Like i said about the boyfriend, you don't want to get back with him knowing that you haven't even given being with this girl a chance because you never know it might be a turning point for you, seeing as how you've never been with a girl it will let you know if you like them and should question your sexuality further. Take the opportunity whilst you have it and then you won't have anything to regret.
Good luck and if you want to talk about it further my inbox is open if you want to talk.