Why Jealousy?

Dear viewers,
Why do people get jealous? Why do I get jealous? Do we always have to want what others have? Why can't we accept the things we got now? I mean I know for a fact that most of us have been jealous of someone atleast once in their lifetime, it's just human nature, it happens. But why is that reason? It's like we don't want to see other people happy, we just want to be greedy and take it all, trust me I know; I hate to admit it but it's true! We see someone with someone or something, and we can't help ourselves to ask "Why don't I have that?" or "Why does he or she get to have that?" I know how it is, I've been there myself. I just wish it would go away, I love my own things, and even though I don't have what he or she has, doesn't mean I have to hate them or even hate myself for not having it (whatever it might be) I want to be happy with what I've got, and who knows I might even receive better one day, maybe not today or tomorrow but one day! So why is it that I mean to act right at the moment, but as soon as I see someone with something I've always wanted and can't have, I get jealous? Am I an evil person for thinking this way? Will there ever be hope for me? I just hope someone out there can understand me, and tell me, why? I just don't get it, I don't want to be "The Green-Eyed Monster" but I can't help it at the same time. What do I do at a time like that? How should I act at a time like that? I just want nice things to be happy, but at the same time I don't want to be materialistic and rely on things that I can't have forever anyway! So then why care so much? Who knows! That's just human nature I guess, it's the way that we are and can't help to think that we mean right, but act wrong, right? Well anyway thanks so much for reading my crazy confusing thoughts, remember to always keep hope alive.... And ofcourse to also keep your head up! Peace!!!! :-)