She is being kind of a bitch. She knows you like her, and instead of saying "no" when you ask her out, she says "maybe someday". She has you on a line so that if something doesn't work out, she has a fallback guy. Forgetting about lunch? Yea, **** that, she didn't forget, she just found something better to do.
You're inexperienced and don't know when to move on. This is a learning experience for you, mostly so because you won't ever date this girl. Here are a couple of rules you can use in the future:
- If you ask her out and her answer is anything but "yes", she isn't interested, you should move on.
- Ask out a girl after you've been talking to them for a couple of weeks tops, don't get all extended crush on someone, just makes the rejection more painful
- Don't rely on word of mouth, it doesn't matter what her friends said, all that matters is what she says, and to your face
There are many simple rules like these, but in this case I'd think of these ones. She isn't interested, stop talking to her, stop wasting your time. She will come back around when she sees you're missing and try to attach a line again because she likes the attention, but that doesn't mean she likes you.
Remember, learning experience, nothing else. Move on when you're ready.
"All is fair in love and war." - Francis Edward Smedley