Feeling left out...

For all these 18 years of my life i felt left out. I am a very family oriented person but due to many reasons i would say i have no family. All my cousins are in touch with each other except me. Not that i didnt try reach them out or asked several times to communicate what happened but they did what they wanted. The only few people i now can depend on is my brother mom and dad and few friends. But even with friends i do feel left out and i want validation every now and then. Recently what triggered me is that whom i call my best friends makes me feel very alone sometimes whenever i go out with them in a group especially. My best friend lets call her x. She is supposedly to get married and proposals are coming in. So there is this one guy who her family liked and she was telling me about him. She got no pictures of him and she didnt remember the name either. She told me not to tell this to anyone even our common bestie this other person lets name her y as she doesnt like the idea of marriage. That was all okay to me. Until few hours back. We have a common group chat there this y person sends in a photo of two guys with their parents. Upon seeing this, person x reacts and after i asked the context person x tells me this is the same guy she told me about and after hearing both of them person x and y making fun of the guy it was pretty obvious that they talked about him a lot. Person x told me that it was very hard for her to find the pictures and the time between when she told me and today is few weeks. Now it is not a problem that person x told person y but this makes me feel very left out especially because she told me not to tell her and then herself goes and tells her and chats about him and i know nothing. This has happened before. I normally prefer talking it out but i think ppl thinks its funny the way i approach. Most of the time they mock me. I know i am a little immature than them but for this i have been made fun of ever since. Its very common to hear i zone out every outing but dont they understand why Should i go and tell her that it bothers me because i dont also think that she does it on purpose.