TL/DR: Part of being an adult is choosing the people you want to share your life with, and choosing who you want to be for yourself. I'm sorry you had to go through such a painful experience but I'm happy for you that it has worked out for the best.
I have had toxic friendships in the past. It's really difficult because a toxic relationship is always a two way street, whether you want to believe it or not. Figuring out what it is about yourself that allowed the two/three/twelve of you to create and engender a toxic relationship is just as important as severing ties with the person/persons, if not more so.
I had a large group of very close friends throughout almost literally my whole life that I slowly realized wanted me to be their version of myself, not my version of myself. What made it a toxic relationship was that I wanted to be that person for them too. I defined myself that way, lived that way for so, so long, and hated myself the whole time. It's very easy for your status or role in a relationship to crystallize into your identity over time, and its nobody's fault necessarily, it's just something that can happen. I can't continue my friendships with them because I know, who I am right now, I'll become that person for them again. My identity is fatr too fragile to risk it. I love them all like they're my family and Its not fair to me, and its not fair to them to destroy myself for a force of habit.
It has taken me two--almost three--years to fully divorce myself and my identity from them. Hands down it has been the most difficult experience of my life, and it has been a much more jagged and ugly and painful process than I ever wanted. Especially because its the group of people and not necessarily any one person in particular, and that I intellectually know that its nobodies fault (except maybe mine). Throughout this time a toxic family member was also in the mix too (I have recently severed ties with that person which was a much shorter and more violent process). It has been so much loss in such a relatively short period of time I have very much questioned whether or not I'm having some sort of mental break (unfortunately I don't think I am). It's almost daily that I go over the whole mess in my head and ask myself if I'm crazy.
I've heard my friends parents say that their 20's were the best years of their lives but holy shit do I hope that's not the case for me :D