OK, first of all, I'm no pick-up-master so it's not like I'm an expert in this kind of situations. However, I experienced things like this my own, so I'll just tell you my opinion.
1. Don't get stuck on this one girl. That's one-itis. I met a lot of girls where I thought this is a girl I can spend the rest of my life with, but that doesn't mean she feels the same (yet).
2. Don't be needy. I know you are in love, but you have to talk to her with a mindset this is just a random girl and nothing is going to happen. If you start building expectations, it will probably fail, so don't do that.
3. Be cocky & funny. Build a frame where you act like you already have everything going on for yourself. Next to that make it sound like she is picking you up.
Surf the net for examples of cocky and funny. The trick is to be arrogant, but as long as it's funny it's ok. Other things I use is misinterpretations (for example I act like all the things she is saying are meant to be sexual.), roleplaying (like you act like she's your sister or your stalking ex-wife, but I'm not sure if you can still use this one) and exaggeration.
4. Look at the situation from her perspective. She already has a boyfriend so why should she go out with you. OK, her boyfriend has a car and is older then her, that's an advantage. The car itself is not so special, but it enables him to drive to cool places and do more fun things with her. The trick is to show her what kind of things you have going on. Hobbies, fun stuff you do, dangerous stuff, ...
I do have to admit that this is a sticking point for me myself. Many cool things cost money, for example travelling, doing restaurants, hobbies like snowboarding, sailing, ... So money can be an issue despite what many pick-up-artists say. Next to that you can do cheap things like long walks on the beach, cooking for her but then again since you're 18 I'm not sure you have a place of your own or a car to drive to beautiful places like the beach. I'm 20 btw and have the same problem. So if you can figure fun and original activities yourself, please let me know.
5. About the boyfriend again. Boyfrienddestroyers are all about finding the weaknesses of the boyfriend. Jealousy, being to controlling that kind of things. Now, I do have to say if he's the kind of person that acts like every day with his girlfriend can be the last one with other words being totally not needy! That this won't be a relationship easy to sink.
Conclusion: What I would do in your situation, is check how strong the relation with her boyfriend is, while showing her what kind of cool stuff you got going on. So she becomes more attractive to you than him.
If the relationship is too strong, just let it go for a while. Stay in touch with her, invite her to fun things, you can even invite the two of them, just to let her know from time to time what fun stuff you do. For example, hey I'm throwing a party maybe you want to come. Like acquaintances do. If she doesn't come don't worry. She'll hear how cool it was from others anyway.
Now, if the relationship suddenly gets weaker or ends, then you have another wake-up call. Then the time has arrived to start being closer again. Oh and try to follow up the relationship more or less through a friend of her or somebody else not by being her primary best friend. Because if you're her "friend" and the relationship ends she will certainly not become your girlfriend. As you know friendshipzone means being screwed!
Anyway I hope my long advice is of any help and let me know what your up to do with it.
ZACK
