To me this just sounds like being shy. Shy people aren't people without the ability to talk to anyone, they just don't do well around strangers. An outgoing person is the life of the party with or without their friends around. I myself am more of an outgoing person. I tend to strike up conversation with people I make eye contact with and have no qualms with being myself in front of strangers. To clarify, I don't think there is anything wrong with being shy, and I'm glad that you are able to let loose with your friends and the people you feel close too. That being said, I think you're just shy but hiding a really fun-loving personality behind that.