How do I know if a girl is "using" me?

[The Green Bastard]

Last night my "almost" girlfriend and I went to the movies, mostly because we wanted to talk about stuff. (If we should date again or not, if you must know) We've went out on and off since last summer and I kind of like her still and whatever. She is always overly horny, no matter what, and on the phone she asked me if I would finger her at the movies and I said "only if we're going out by then" and she accepted. However, when we met there, we went straight in and didn't do much talking. At first it was a bit awkward, then we made out and went further from there. I want to be her boyfriend, but I'm wondering if she is just using me.

Thanks.

[EleXtroSeXual]

Sir, shes probably using you for sex :O!!

[The Green Bastard]

That's not always a bad thing, right? xD

[EleXtroSeXual]

Is it a bad thing.

Supposed to be about love n shit.

[The Green Bastard]

Damn. You're right. I should of stuck with my promise to myself.
I said I wouldn't do anything with her unless we were going out.
I feel so ashamed. Especially to do shit in a cinema...