Toxic Trio

I have a bit of a friend crisis. I am in a toxic trio friendship where one girl (we’ll call her Sam) is obsessed with this guy (we’ll call him David) who is friends with both of us. Basically she’s buying his friendship by driving him around everywhere, paying for dinner for them, etc. She plans things without me and doesn’t invite me, and then openly tells me about the fun things were doing together. David doesn’t refuse her though. He still talks to her and hangs out with her without me, but he doesn’t like talking about it, almost like he’s trying to hide it from me.I found out today that she bought the two of them front row tickets to see a Broadway show-without me. She told me about it today, and told me not to tell him because “it’s a surprise.” I hope I’m not overreacting, but I’m pissed because I’ve known her for over a year and a half, and one time I literally talked with her on the phone for four hours when she got deferred from her top college.he’s the new kid and she’s known him for only a few months, but i know she would never invite me to do something like that with me. What’s worse is that they still actively seek me out, almost like they’re using me for some kind of validation. They both compliment me and say I’m beautiful and talented and laugh at my jokes...and then they go off and have dinner over the weekend. They feed off of each other’s toxicity, and sometimes it feels like he’s just using her for a ride (he doesn’t have a license) and she’s using him for validation, and they’re using me to make them feel like good people, and I’m using them to feel better about myself because they always compliment me and are nice to me and stuff. It’s just a cycle of toxicity, and I don’t know how to get out of it because we all go to high school together, sit at lunch together, etc. I don’t want to seem rude, or like the girl who just cut off her friends halfway through senior year. At the same time, I can’t continue to be treated like this. Any advice for this toxic trio?