No, you're not losing it. I understand what you mean by feeling like the outsider. I had a group of girls in high school that I was very close with and they all are off getting engaged and married and kind of left me behind. You are very strong to go to that party, so I commend you for that. I was invited to some get togethers by those group of girls and I declined because I got fat and I wasn't as pretty and skinny and sexy as I used to be. I see them on Facebook, and noticed that they have "replaced" me in their group by adding some other girls.
It makes me sad and got me upset so I deleted two of them but kept one because she was always nice and didn't do anything to me. But, she is friends with the others so I see them all together in group photos and it still bothers me that I am not part of their group anymore. So I know what you are going through. My answer to that is, make a new group. You can start here. By posting and playing the games and joining the community. Make one or two comments or join a chat and you will find you are not alone.
Welcome and don't be sad. I look forward to seeing more of your posts.