Human Relations

So I went mini-golfing today with the golf team and it got me thinking about the way I connect with people. I tend to act differently with different groups and in different situations without even thinking about it. I'm afraid that I'll be seen as two-faced or multi-faced when I don't mean to be. Well, I'm naturally an introvert-- I know at least that much. Up until recently I didn't really enjoy hanging out with my friends outside of school and I actually used to make up excuses for not going. When I'm around people I don't know, I find it difficult to muster up the courage to say hi, and even if I do, I can't carry on the conversation after that. I've noticed that there are only certain people that make me put my introvertedness aside, but I wish I could be social with everyone. Like at church, I don't really talk and I go home right after the service ends. I guess I have 'friends' who I feel comfortable sitting next to and talking to, but really, I don't really know them and I can't be myself around them. I've known these 'friends' for like 2 years. But around the golf team, who I've known for only a year (except the 2011 people, who I've known for longer) I get really talkative and fool around and stuff.
I think I really started thinking about all of this the past year. I got closer to like 4-5 individuals from different cliques and I really want to know more about them. All I did was share a few words and laughs with them in the classes I had with them, yet we got so close. But at like Key Club events, I want to get closer to everyone in the division, but I can't seem to get myself to be myself. So all I do is say "hi" or exchange some small talk, but I never get the feeling of "closeness". Similar things happen in school. Like there are some people I've seen everyday for the past 4 years yet I feel like a stranger and we don't even say "hi" when we walk past each other. I always look around the room and think "I want to know him/her more" but I'm too shy or scared to start a conversation. I wonder if everyone feels like this, or if its just me. I'm even awkward around my family. Since I didn't start going out with my friends frequently until like highschool, my family thinks I'm really shy and quiet around others. So when I'm with other people my age and a family member is nearby, I change into their image of me and become quiet. I think this is part of the reason why I can't be myself at church.
I don't know, it's really frustrating because I know that I can be outgoing, but I can't seem to act equally with everyone. Some people make it seem so easy to make friends, but it's pretty hard for me most of the time. I hope that I can change by senior year. I really want to know everyone at Oxford, especially our class. It pains me when people say "oh, he's/she's so nice" but I don't know that person. It seems like a waste to have all these great people around me but not get to know them personally and have them teach me.