cutting off my “best friend” before her 21st birthday

so this story requires a lot of context, for the sake of my time and yours I’ll keep it pretty condensed.

(i will be calling my ex-bsf M)

I recently completely cut off contact my “best friend” after we’ve been friends for around 14 years. While me and her were inseparable for about 9 of those years, through recent times she entered a relationship with someone i really never got along with. At first, the anger was definitely targeted towards my lack of adjustment to not hanging out as often (i was a teenager during the start of this downturn), and more at the fact that M had stopped reaching out as much or even responding to texts really. Through this I had multiple conversations with her about how this made me feel, and while she would empathize nothing really ever changed and no effort was being taken on her end of our friendship. I would express to her that when we hung out I’d prefer for it to be just us or other friends, but somehow her girlfriend would always end up involved in plans. After a while, i kinda just got used to it and let it happen. My anger started to progress further towards M’s girlfriend when M began telling me that she would treat M terribly quite often. Well, quite a few times during these hangout we would all drink (to a far extent). During these times they would ALWAYS get into a fight in front of me, and by always i mean i can’t remember a time where an issue didn’t occur. Of course I’m not a relationship counselor but i would always console M during these arguments and somehow they’d wake up and act like everything was fine. These moments made me extremely uncomfortable as one can imagine, because while being plastered I can’t really intervene with a clear mind and i believe i shouldn’t have to. Especially when most of the time nobody would really tell me what the fight was about. M’s mom would sometimes know about these occurrences, and would encourage her to stay away from the alcohol. One of these fights occurred when all 3 of us were out of state for an event, and we were all at an 18+ club (we’re still all under 21 at this point, hence the title) and the night wound to them screaming at each other in front of the club while I was bawling asking them to stop. Fast forward and it’s the weekend before halloween of this current year. M invites our friend group to her and her girlfriends apartment for and early halloween outing. Everything was going relatively well at the beginning of the night (as it typically would) but by the end it was a complete shit show for the 500th time. I will attempt to recount the events as best i can, as i was pretty messed up this night and had the event retold to me from a more sober friend. The group of 5 of us had all gotten dressed up to go to another 18+ club, we got there had a good time for about an hour until all hell broke loose. While me and one friend (S) were dancing, the others decided we should go home. While M begins ordering the uber her girlfriend walks up to her and starts bickering in a “what’s taking so long” way. M’s girlfriend then enters the dance floor and starts dancing with a girl she knew from softball. This obviously makes M upset and so S tells her to ignore it and starts pulling her to dance with us. M walks away from us and sits in the back relatively near where we were dancing. I have dealt with their arguments countless times before this so honestly, yes, i was ignoring it. The uber arrives and i later find out that while we’re walking to it M starts running away from another friend K while she’s attempting to relieve the situation. We all make it into the uber and make it back. I go into the bathroom with S because i needed to go and also needed to rant. Me S and K then began hearing screaming coming from one of their bedrooms. I swing open the door and lo and behold i see M on top of her girlfriend swinging. I pull M off of her and M starts screaming at me and i began screaming back and pushing her away from trying to exit the room because at this point she had given her girlfriend a panic attack and she would not stop crying screaming “get away from me”. I sit down on the bed in front of M while she’s still actively screaming at me and i begin calling my boyfriend to come pick me up because i couldn’t stand being there anymore. M then proceeds to bring up the fact that i’m “calling the boyfriend that cheated on me” which albeit was a long time ago but is indeed true, and I’ve never claimed to be perfect nor have i ever said my boyfriend or relationship was perfect. I begin drunkenly laughing in her face and walk out of the apartment and sit on a table in the small “lobby.” My boyfriend was about to leave to pick me up which was about a 45 minute drive from their apartment. S then claims she is sober enough to drive us home (shouldn’t have done it i know, we typically never do this). All of us including M’s girlfriend then leave leaving her alone in the apartment which i still feel bad about even after all of this. I blocked her on everything and the next day she had texted S many “apologies” for ruining the night claiming she remembers nothing, which I’ve heard a million times over again. M texted me apologies too which a few i received on my iPad because it didn’t register that i blocked her number. Well her 21st birthday is coming up next week, and i just feel so wrong not being in contact with her to celebrate as we’ve been friends basically our whole lives. But i just can’t push pass the fact that she has put me in these terrible (honestly traumatizing) situations so many times and doesn’t have enough respect for me to either hang out ALONE with me or stop getting into these altercations in front of me. I also can’t believe that i put up with their shit for so long just to have her personally attack me with no regard. I was also really blindsided to see her as the one physically harming her girlfriend, as i was under the bias that she was innocent in this toxic relationship.

AITAH (i guess would i be) for not celebrating or telling her happy birthday?