I've having bad girl trouble?

This girl just won't open up to me. Well, she has, just not in the way I want her to. Her name is Julie, and she doesn't suspect that I like her. I just started forming feelings for her a week or two back, and I always sit at her lunch table with all of her friends, which are ALL girls. Yes, I know, GIRLY, but they are awesome and pretty cool. She has a boyfriend named David. Her boyfriend is really perverted, and he did stuff with my ex that I just told her about two nights ago. She said: "Ok thanks Nick" and that was the end of it. I'm surprised she didn't even get the slightest of mad at him today, and I didn't tell her that just to get her to break up with him, I said that because I don't want her getting herself into something she'll soon regret...and I'm really afraid he may force her to do something. Today at lunch she sat my me, and I was so happy. Does this mean anything? I text her a little more than I should...I texted her for a while two days ago, and I texted her yesterday and I think I bothered her because she was trying to do her homework. I told her I was really sorry...no text back. I haven't texted her today. And she likes to send one-liners or one-word texts back to me, I hate that. I feel like I'm being annoying. I like her...a lot. I really don't want to screw it up. This feels a lot different than most girls I like. How do I get her to open up? Should I sit somewhere different at lunch? Get her to like me? Any tips/advice? NO WEBSITES. Just personal experience please and thank you! If this helps, I'm 15 and she's 14. Her boyfriend is...14 I think? Thanks in advance! :)