AITA for cutting off my college friends after they used me for years?

I've had three close friends since the beginning of med school—let's call them Yellow, Green, and Purple. We were a study group and did everything together. I'm the oldest (24), since it took me a while to get into med school (I'm from a Latin American country, and it's very competitive).

Ever since the first semester, I noticed I was the one doing most of the work when it came to group projects. At first, I didn’t mind because I take my studies seriously and assumed they just relied on me because I was more organized. But by the second semester, it became obvious they expected me to do everything—powerpoints, research, formatting, even structuring the presentation so they only had to memorize a few lines. They always got full credit, just like me, despite barely contributing.

Last semester was the breaking point. I had six subjects and had to do seven major group projects. Once again, I did them all alone. Green would occasionally offer to help, but when she did, she’d just copy-paste from ChatGPT without even trying to reword it. Yellow didn’t bother at all.

What made me finally cut them off was a specific subject we had to take—an indigenous language course. I struggled a lot with it, and everyone knew, including Yellow and Green. Meanwhile, I was drowning in group projects and trying to study for this class.

One day, Green casually told me she had spent the entire weekend at Yellow’s house just studying for the indigenous language midterm, I let it slide because i thoght it was a one time thing but then for the final, she mentioned again—completely casually—that they had been studying together since Thursday. (we had the subject on Monday ).

That’s when it hit me. I had been doing all the research, all the projects, carrying them for years, while they never once offered to help me with my struggles.

To add insult to injury, I missed one presentation (out of seven) because I didn’t get the minimum points to present. I let my group know in advance, gave them my part of the script, and made sure they had everything they needed. I had never missed a presentation before. Later, I found out from another classmate that Yellow had privately messaged her saying she "expected" me to drop out, i beg your finest pardon????

That was the final straw for me i made the decision to distance myself. I will still acknowledge them when I see them, but I have no intention of working with them again. Right now, I’m taking an online summer course where Green is also enrolled. She has sent me private messages, but I haven’t replied. Next semester, I’ll have classes with both Yellow and Green again.

Purple, who has seen firsthand how much effort I put into everything and how things fell apart, has stuck by me. However, she’s taking different classes this semester, so we’ll only really see each other at lunch. That means I’ll either have to make new friends or spend most of my time alone.

I don’t plan on being rude, but I can’t shake the guilt of cutting them off without an explanation, any recommendations on what can i do?