占有欲 - Possessive

I am a possessive person. That is something I can never deny no matter how much I want to. And to make matters worst, I am selfishly possessive.
I can't take it when people take what is mine (or that I think it is mine). I get so frustrated, unhappy and jealous that I become emotionally unstable (keeping to myself the whole day, snapping at people when they try to be nice and saying things that I regret later). And I regret doing all the things that I do, making me more depressed and frustrated. Finally, when I can finally look pass the wrongs that I have done, I start the process again. Just because I want the things that might or might not be mine and getting angry at the whoever that is stopping me from getting it.
I hate it when people are happily talking without including me in their conversation. I hate it when they forget to invite me to whatever events that they are hosting.
I hate it when they choose to ignore the fact that I am there and that I also will like to know whatever that they are sharing with each other so I wouldn't be in the wrong due to the lack of information.
I hate it when they just don't think that I am important or I think that they don't think I am important.
I need to feel needed to feel safe. I need to be in every part of the lives of the people I know and I don't care if they want me there or not even when I know that there is no way that I can do that.
I want everything that I like and I want all the attention that I can get. Yes, I am greedy for everything that can bring me comfort.
I am possessive, especially towards the things and people I like and love. I know I only think about myself when I say this but this is me. I hurt people when I am unhappy and thus I hurt myself. I need the attention to feel secure. I can't stand one minute waiting for someone because I can't stand not being needed for that one minute. That is how bad I am at needing attention. And I feel that I can only gain attention by possessing what/who is giving out the attention to me.
I need to learn how to stop this feeling or at least control it before it eats me up and making me even harder to understand/communicate with.
Hope I can learn from my mistakes and be a better person in the future.