I don't feel like I want to share stuff with my friends
Why would you not want to share with your friends?
I prefer to keep everything to myself rather than share with friends.
Sharing with others is a nice thing to do.  Not sharing can be perceived as selfish.
People don't like me and I don't want to share my life with people.
But as they say, sharing is caring, so if your friends share with you, that means they care, so it is expected that you reciprocate the same, or they might think you are selfish and don't want to be friends with you. So in order to avoid losing friends, I suggest you try to share whenever you can, even if it's just a piece of gum cake. That will make people think you are generous.