꩜ .ᐟ i need advice/feedback!! +AITA?

So i became friends with this girl in 8th grade, we’ll call her Z,  (I’m a junior now), and she wasn’t really someone I knew and I had recently broke it off with another friend I had since 3rd grade (because of another person…😐) so I didn’t really question how suddenly she just sort of invited herself into my friend group. Honestly I don’t ever want anyone to feel bad or unwanted and so I stuck especially close with her, and sort of in a messed up way replaced the space my old friend had. 

Things were alright in the beginning, until she sort of started becoming passive aggressive…So we had this thing called TREPS in 8th grade where we just made small business in groups and sold them and stuff, the class I had didn’t do TREPS so I wasn’t a participant, but I remember my other friend partnering with Z and they made handmade jewelry and stuff. It was alright, I mean I was just there bc my class was a free period then. So my friend wanted to go check out the other stands, and Z was sort of pressuring her to watch the stand, meanwhile I suggested they go in shifts, since I also wanted to go and check the others out (but I didn’t wanna go alone 😓), then I remembered Z arguing with me, not really the specifics except I remember when she finally said that “nobody wants me”, and I just sort of remembered losing it, and tearing up before my friend took me upstairs to cool off. I felt like in that moment, I really missed my old friend who broke it off with me, and i did. Since then, she hasn’t apologized or even admitted she said that, but excused and told others that I was “scaring away customers,” 

In freshman year, I sort of moved on from all that…But she just sort of got worse. She comes off as condescending and I feel like she looks down on me. She’s really smart though, and athletic, so it just rubs me the wrong way. She would make small “jokes” which were always totally unprompted, and whenever I asked her for help during AP World, she’d make a fuss about how stupid I am, and how I was going to get a 1 (scores 1-5), because I asked what contextualizing was.

Last year…I stopped considering Z as a friend, moreso a transition between acquaintance and friend, we still had some classes together. But, we started a club together..and let me tell you, she does literally NOTHING. I go to every meeting, and a day before to talk to our advisor, and I plan the activities while she just comes in and does the talking. But I digress…That’s not what bothered me the most. What bothers me the most is when we wanted to start up our schools pre-med club again, because it was discontinued last year, and this girl did the bare minimum 🧍‍♂️…

So the whole situation was that the bio teacher who was supposed to be the advisor was going on maternity leave, and there was a three month long issue due to budget and stuff…I was actively seeking out an advisor (and found one!), while she never once asked me anything about the club since we first proposed it. So..naturally the previous planned advisor (who was helping me find another) forgot about her too (😭), so I decided to put my other friend on, who wants to pursue nursing…But here’s kind of where I feel guilty. I feel like I kicked Z off the whole process, and ditched her…But I also feel like I listened to my gut, since she treats me like crap and doesn’t do anything for the our other club. 

Since then, I got an advisor for the pre med club, and sort of avoid Z…But I still feel like I might be the asshole for ditching her with the club. 
I know this was really long, but please give me actual advice!!! 🙏 I genuinely need a way to secure my self validation, but I don’t want to make Z feel abandoned or cheated.