Replying to What is going on in this girl's head?

I asked a particular girl to homecoming this year that I like.  She is aware of this and she said yes.  Im all excited and happy because, well, I like her.  Out of the blue, like 3 days after I have continually been seeing her at school with a guy that I know she used to be friends with.  So Im like ok, whatever, until this goes on 3 straight weeks and I found out they were hanging out last weekend, which she lied to me about, because I was going to stop by her house and say hi, but she said her parents werent home and I couldnt come.  She still claims that she wants me to take her to homecoming though.  What is going on here?  Can someone translate this please. Tldr: ask girl I like to homecoming, she says yes, is now talking and hanging out with another guy, still wants to go to homecoming with me.