Balance.

It's silly how jealousy is taken advantage of in so many ways nowadays. The main way between teens? It's used to make someone you (usually) like feel bad. Everyone does it, I do it, you do it, we all do it. You say something you know they don't want to hear just to make them jealous and it grows. First it's something small then it gets larger, finally both sides of the relationship does it. I don't mean as in people that are going OUT do this, I mean people that LIKE each other, or one likes the other.
Why do we do this? It's somewhat psychological. You feel deprived of the other person and feel bad about it and in return, you try to make THEM feel bad too. Most people don't even do this purposely, it just starts to happen then it flows on from there. You want them to suffer so they know what's up. Really though, we're just asking for attention from you, aside from the making you feel bad thing.
It's like a lot of other things in life where you expect everything to be fair: exactly HALF a piece of a sandwich, he hurt me so I'll hurt him back, I know he's cheating on me so I'll do it too, and, the one that befits this case, I'm hurting because of her, and she should feel the same way. I just think it's hella strange how the human mind/emotions combine to do such a bitchass thing. Though I try to be the better person in most cases, in this category, I fail. I am guilty of doing this a lot, even right at this moment maybe. Whether the things I say really work and make the other person feel bad, I don't know. But I honestly hope that they don't. I don't want to make someone feel bad just cause I assume they're trying to make me feel bad. I have no right to do so and it's just a mean thing to do. So try not to attract attention in this way. If you really want the attention of a loved one, let them know how much they mean to you and be there for them, don't put them down for selfish reasons. =]