Am I Overreacting? Ignoring friend after she left me
Hello, this is my first time posting on here! TLDR at the end, for context, my friend and I met in the beginning of the school year back in august. We quickly bonded because she (17f) had just moved here from out of state a month before school started. I (17f) moved from the same state 5 years ago. We liked the same things and had the same humor, so we became close. At the same time, she began to form quick friendships with popular girls above our grade. I know, it sounds petty, but please keep reading. Last week, during the break for our AP Lang exam, she asked me to go out with her after the exam ended to which I agreed. After it ended, I bombed the essays pretty badly and was in a tearful mood. We got into her car and she asked me where we should go, I told her I had no money so anywhere. I began to speak about the exam before she told me that she actually planned on going home to eat. I was surprised because we were already on the road when she brought up going home, and I said oh okay, cool, we can chill there. She asserted that she wanted to eat with her mom, to which she asked me where I parked my car.
Fast forward, she dropped me off at my car and asked me what I was going to do when I got home, and I said "cry". I got into my car and began to cry on the way home. She sent me a heart emoji text saying "sending love" a few hours later. We hadn't spoken since that wednesday.
Sunday came around and I noticed she had been non stop posting with her older friends. I felt disheartened because she'd told me that our friendship meant a lot to her, that I was her closest friend, and she once mentioned that I was her only friend in our grade. We were super close, went out a lot, and we both confided in each other about our insecurities and close secrets, things that close friends do.
I thought it was fine because as I said, she's very carefree, and doesn't necessarily overthink at all, not in the capacity I do. My concern is that on sunday, I reached out and asked if she was mad at me, she said "LMFAOOO" "no" and invited me out to lunch. She stood me up and apologized because she was busy. During our math class, we usually don't speak as we have separate friend groups, but she only tells me hello when her older friends are gone. My point is, am I her backup friend? Am I embarrassing myself by putting a lot of effort into our friendship? I've noticed she always posts with them but not with me, even though her and I go out at the same rate she does with her other friends.
If I'm being honest, i still feel hurt about her dropping me off at my car, even though neither of us brought it up. I didn't say anything to her about it either. We didn't speak again since sunday until she texted me today saying, "im not mad at you, sorry for being distant, I've been super busy and stressed"
TLDR; best friend of mine stood me up twice recently, and I've begun to contemplate our friendship. She constantly hangs out with her senior friends and posts them, but when we constantly hang out she never posts me. Friend claims she is busy and stressed but posts hanging out with her friends during her stressful times. (pls read context if possible)
I feel really embarrassed and I plan on distancing myself from her starting today because I feel I am only her friend for the connection to our grade + being a back up sort of friend. Am i overreacting?