u/SubjectButterfly7588

I have been in a small group of three friends at my high school for a few years now. One of them is in a friend group at another school. They have their own friends, too. My two friends and I have been part of that group as friends for a few months now. But one person from my original friend group (me and the other two), Thom, has been acting weird these last few months. He excludes me from the large group and only makes nasty comments to me. He acts jealous. Nobody knows that I feel this way about him. I have to start an internship in a month and I can do it abroad. I asked if I could bring two friends along (two from my school) and that is allowed. I asked for both of them because nobody is allowed to know that I don't like the other one. That is because we are all going on vacation together (with the large group) in a few months, so I need to keep them as friends. Now I want to ask the friend from school whom I like if he wants to come along, and then I'm going to tell my two friends that only one person is allowed to come. But maybe he doesn't want to or can't come, and then he will suggest me to ask Thom. Or he might even tell him that I have a place for a friend. But I don't want him to come; I think it is clear why. What should I do?