I've felt this way before. Its mostly because I struggle with conversations. I feel like there is some big secret that I'm missing out on and because of that I cannot talk to people normally. Especially because we humans are supposed to be social creatures.Since I cant do that as easily as others I feel like I'm not normal.

Since your friends are actively attempting to invite you out to places and have you join them I'd say you might be a bit paranoid in that respect since you believe they don't like you. You have to keep in mind that if they didnt enjoy your company they wouldnt go out of their way to talk to you or invite you to places. I know its hard to just ignore those thoughts, Ive had them too, but I suggest you just take your friends at face value.

As for some advice, I don't think Ive got anything good to say. I havent really been able to get over my little social anxiety problem when it comes to my friends. With strangers though I've gotten to the point where I don't care what they think of me. As long as im being friendly if someone doesnt take to me or conversation doesnt go the way I had hoped then I just shrug my shoulders and move on. I didn't really do anything to get to the point, it just happened one day. I will say though that I don't think you should be trying to close yourself off from people. That doesnt do anything but stunt your social skills.