<human>: Okay Reddit, here goes.

An old friend of mine who I hadn't seen in a while calls me one day and asks me if I want to go to prom. We're of the same high school class, but she dropped out and is now in community college, a year ahead. This would be her senior prom, but she can't go without a date, so she asks me. I told her I'd think about it, then called her back and said I would. 

She's really interesting and I'm really into her. We've seen each other almost every day for about two weeks, and I was pretty sure she was into me too. Well we were supposed to hang out and watch a movie at my house today, but she texts me and casually brings up that she has a boyfriend and he would have to be here too, for logistical reasons. 

I didn't realize she had a boyfriend. I'd never asked her about it, but by the way we were acting towards each other I'd assumed she didn't. We were really flirty (I would be upset if I was her boyfriend) towards each other and I feel sort of betrayed. 

I've already agreed to go to prom with her, but I don't know if I can do that without having feelings for her then. I don't know what to feel. I'm honestly pretty inexperienced with relationships, but should I have seen that coming? What should I do now? I'm pretty committed at this point, but I don't know if I could follow through now. How should I handle this?

Can you succinctly summarize the text in 1-3 sentences?
<bot>: Girl asks me to prom, I really like her and though she felt the same but it turns out she has a boyfriend. What should I do here?