I think love definitely starts with a strong attraction (duh) -- but how we respond to that attraction is our choice. Sometimes, we just go with the flow (so perhaps it doesn't seem like a choice?); but attraction can't become love (or even infatuation) without some work on our part.
For example, a one-time spotting of a person who's attractive to us won't produce love (or any kind of relationship). We have to act on that attraction and try and find the person again, spend time with them, foster the attraction even. It's like stoking a fire, no?
When we're teens and our hormones are all over the place, attraction happens very quickly, very intensely, and it fades just as quickly (at least, in my experience). For that reason (among others), I'm a fan of casual dating as teens -- the opportunity to spend time with the source of the attraction without any pressure to turn it into something "important" and lasting.
I still cringe when I see (or hear of) teens marrying young (as in, while they're still teens). It's part of the fairy tale image, perhaps, that many young adults think that once they've married that 'perfect' person, they'll never be attracted to anyone else again...sadly, that's so not true!
Looking at attraction from an adult point of view, I get a little impatient when I hear stories (usually on the radio) of men or women who leave their spouses/families because they've 'fallen in love and can't help what they feel.' Um, yeah, you can. I want to say to them, "You know, you were attracted to that person, but attraction isn't love. And you have to act on that attraction in order for anything to come of it." So they could help it. They made the decision to fantasize/dream about the other person; to find ways to meet up with them, even if it looked innocent; to talk to the person. In short, they made a path for an affair in their life, and although it began with that spark of attraction, the rest was not only a choice but a very clear determination.
I suppose, after reading this, it sounds like I hate infidelity -- I don't. I mean, I don't think it's a good thing, but I'm not really a black and white thinker. However, I do hate the excuses I've heard people offer for their infidelity. You don't just fall in love at first sight and lose all control over your ability to be faithful. You have to find ways to cheat -- it's a decision. And yeah, people might have good reasons to make that decision (reasons that are logical, at least), but they're still making a choice.
How does this play into my WIP? Well, that would be telling...:) Clearly, it's about young love (with a heavy dose of attraction). What say you? How do you feelings on adult romance affect how you write for teens?