Tick, you have unrealistic expectations of her. I'm not saying that you're asking too much generally, but that you're asking too much of her. She's bound to disappoint you.
If you could get the idea into your head that you don't actually need anything from her, you'd be happier. She's a limited person, just like everyone else on the planet. This has nothing to do with that other guy, and ultimately, not much to do with her. It's about you and your desire for attention from her.
I remember being 16. It wasn't easy. I was so involved with my friends, it was like I hardly existed without them. Later, when I moved away, I started reading a whole lot more and writing, too. I became much more self-reliant. I suggest that every time she disappoints you, you consciously choose to do something for yourself. Learn to not need her so much.