I have my group of friends who all sit on the same lunch table, at the beginning of this school year three of my other friends (two I have been friends with for 3/4 years and another of one year who was only friends with me , not the others on my table). I will call the friend of one year 'X'.
X, who was only friends with me, would come to my table to speak to me and wouldn't even stay unless she could sit next to me. Since she has been sitting at my table one of my other friends (will call her Y) keeps sucking up to her, she always tries to go and sit inside with X and leaves me on my own as we arent allowed to go inside that classroom unless we take that subject which I don't, Y is always asking where X is even when X is okay because she is with her two best friends , today Y even stopped eating her lunch midway and rushed to get up from the table because X wanted someone to go to the canteen with her, even though there were two others (me and her best friend) sitting there with nothing to do. She has even tried to arrange a cinema trip with X without asking anyone else, everything was even discussed in front on our group. She keeps making stuff up about how X's dog is a breed she really likes and she always comments on X's instagram photos about how great they are, I think she is just saying it.
I know I seem unreasonable but she wouldn't of been friends with X unless X was friends with me. I don't like how she sucks up to her all the time and is trying so hard to be best friends with her. I don't want to be pushed out the way because I get on so well with X and I don't want this other girl getting in the way of it, it is like I can't even have a conversation with X because Y won't stop talking to her.
This is genuinely upsetting me and I really don't mean to come off jealous or annoying. I would really appreciate some advice on how I can keep my amazing and caring friend wanting to spend time with me without the other girl stealing her away.
What should I do?