You don't know what level of yourself you are comfortable sharing with people. You love to hang around with people. You love to be a part of plans and fun events and you consider yourself fun but the nagging, permanent feeling that people don't like you or don't want your company is paralyzing.
You think about this probably too much.
You don't go anywhere you weren't explicitly invited. You don't hang out with people unless they specifically ask you too. You are not comfortable assuming a level of friendship with people. You need to be clued in. You've been burned a lot by thinking you were closer to someone than you think
Because you've been burned, you hang on probably too much to the people who do tell you you're wanted around.
Then you start worrying that you seem clingy or desperate or overbearing or like you're trying too hard and it's because you are, you are trying to be fun and friendly and be well recieved because you are so, so lonely at the end of the day, even if you aren't alone and that loneliness is crippling, it haunts you so that during the day you have small panics where you are anticpating the impending loneliness and then it starts creeping on earlier.
You see the people you know going out and having great times and living life laughing, and you are sat at home by yourself and you turned the light off because you don't want to even think that maybe someone can see how depressing your sad little empty life is. You feel like you are the friend from high school that you 'know' but never talk about or whose interests you have any inkling about. You feel like an 8-hour friend, someone to shoot the breeze at the watercooler with about nonsense and then say goodbye to.
You are like a fortuneless fortune cookie. I guess it's nice to have but it's really not the important part of your order, and there's nothing remarkable about you.