Perhaps you are very introverted? I don't think being quiet or secretive is always bad. There are times, places, and people that it is right to share with or speak to. We shouldn't worry if we don't feel pressed to tell everyone everything about us. However, a close friend can be very important, I have several friends who are closer to me than the others, whom I usually talk with about selected topics. Perhaps this may help? But, don't worry about being quiet, it's a good thing not to feel the need to over-share.
It's also quite possible that some of your friends may care about you more than you think.
As for why you are alive, hun, I don't know if any of us know the answer to that question. As for me, I live to find out why I am alive. What is our purpose? the point of living? Some people turn to religions for their answer, some people drown the question, only to have it come back to haunt them later, I think we each must discover our own purpose for ourselves.
I can tell you, however, that different people would see you in different ways. Some may think of you as bad, others may love you and care for you. I don't think you are a bad person, because I don't believe in bad people, and because you are asking this question of yourself. If you are asking, 'am I bad', questioning your actions, I think that says quite a bit about how good you are.
That is my belief.