AITA for skipping my sister's wedding because my gf wants to break up?

I am a 24 year old man, my sister will turn 30 in two months, and she is getting married to her high school sweetheart. My parents took pride in how close I am with my sister and how supportive I am about her decisions, and while both facts are technically true, they are not entirely accurate. You see, my sister is an extreme narcissist, and she is very manipulative, so the reason I am "so supportive" of her decisions is that I have learned to live with whatever she wants if I don't want to be constantly undermined and belittled. The reason we are so close is that she knows how to be extremely nice when it comes to getting me to do something for her.<br><br>She has always used our closeness as a means to guilt trip me into doing whatever she wants. So she lied to my parents about how close we are and how great of a brother I am to her, and they believed her. And that's fine. What's not fine is that whenever I disagree with her about something, she immediately goes to my parents and complains to them that I am being a "jackass" and that she's "lucky to be marrying her 'soon to be husband' who has treated her so nice". She has never even dated him, they have been in a relationship since high school, just like me and my girlfriend.<br><br>&#x200B;<br><br>Speaking of which. We were supposed to go to a party together last weekend, but my gf had plans with her cousin. So she said that she didn't have time to go, but that I could go and have fun, that she would have plenty of time in the future for us to have fun. I knew that she was lying about making time for us in the future, and that she has been planning to break up with me, I knew that for a while now, but I didn't have any proof, so I couldn't bring it up to her. But then she said that she was busy and that she already knew that I was going to the party, so I said that I wasn't going, and she said that it was alright if I went. I said that I wasn't going and that we were going to have fun together. Then she broke down and started crying, saying that she knew for a while that she was going to break up with me, and that I was a great boyfriend, but that she started talking to her cousin again after they both became adults and realized they had a lot in common, and they became very close friends, and that she's always made plans with her cousin over me, and that she was glad that we were going to break up now, before she had to choose between me and her cousin at our wedding, or between our kids and her cousin's kids in the future, and that she wasn't trying to make me feel bad, and that she already talked to her cousin and said that she wasn't going to break up with me until we graduated from college together. She said that she was going to break up with me anyway, but that she didn't want me to go to the party while she was with her cousin, because it would hurt her too much to know that I was having fun without her. She then said that she was going to stay single for a while and that she didn't know if she was ever going to get married.<br><br>&#x200B;<br><br>I was devastated, and I started talking to her and begging her to not break up with me. Even though I already knew that she was going to break up with me, I didn't expect her to dump me without even graduating college together. She started crying even harder and saying that she already made up her mind. I didn't want to make things worse for both of us, so I said that it was alright if she wanted to break up with me. She went to her cousins' house and did whatever it is that she does when she's there. I didn't know what to do with myself and I was in a terrible mood all last weekend. And it only got worse when my sister called me and asked if I was going to come to her wedding. I said that I didn't know because my girlfriend just broke up with me and that I wasn't in any shape to be at her wedding, especially considering that she's marrying her high school sweetheart. She said that I was being a jackass for thinking that her wedding was about me, that I already missed the bridal shower and that mom and dad were already worried that I might not show up to the wedding. She said that even my soon to be brother in law's younger brother was going to the wedding, despite the fact that his gf broke up with him a few months ago. I said that I wasn't him and that I couldn't go to her wedding and that she should understand how I feel, considering that she is my "darling baby brother" and that she knows better than anyone how I feel, because she is so close to me. She said that I was being a brat, that she already said goodbye to her youth, and that nothing could make her happier than to see both of our families together when she starts her life as a married woman. I said that she was being selfish because I already said goodbye to my youth, and that I was an emotional mess right now and that I was sad and grieving over the girl I loved for most of my life, and that she wanted me to go through all of that pain and sadness while celebrating her marriage to her high school sweetheart, and that it just wasn't fair, and that I wasn't going to go.<br><br>&#x200B;<br><br>She started screaming that I was a jackass and a brat and that I was being selfish, that the world didn't revolve around me, and that she was very hurt by what I said. She said that she already told mom and dad about this, and that they both agreed that I was being a brat and that it was so immature of me to say that I already said goodbye to my youth. She said that dad was furious with me and that he's never going to give me any of my inheritance if I don't go to her wedding. She said that I was being immature because I didn't even have a job and that I didn't deserve any inheritance anyway. I hung up the phone. I didn't want to talk to anyone from my family, so I just turned off my phone and went to bed.<br><br>&#x200B;<br><br>The next morning I turned on my phone again to check the time. And I had over a hundred missed calls from my parents and sister. I turned off the phone again and fell asleep. When I woke up again, I had even more missed calls from my family. I turned off my phone again and went to sleep, deciding to not talk to anyone from my family until they learned to respect me and my decisions.<br><br>&#x200B;<br><br>They have been spam calling me ever since. It has been four days now. My parents know how to get into my apartment, but they didn't come and talk to me yet. They always spam call me without stopping. I turned off my phone again and went to sleep. I don't want to talk to anyone right now.<br><br>&#x200B;<br><br>The wedding is in 4 days, but I'm not going. My family has been spam calling me for four days without stopping, and I have already missed a week of classes. I don't know if my gf is willing to get back together with me if I go to my sister's wedding, but I don't think I am legally an adult yet if I have to go to a wedding that I don't want to go to just to keep a relationship with my family.<br><br>&#x200B;<br><br>Edit: So here's a little update. After I posted this, I went to sleep. When I woke up, I turned on my phone to check the time, and my mom called. I picked up the phone call. She said that she and my dad came to talk to me, but that the doorman wouldn't let them in. I asked her how long they've been here and she said they've been here since yesterday morning, and that they slept in the car last night. I asked her where my sister was and she said that my sister stayed home. I asked her why and she said that my sister already knew that I wasn't going to change my mind and that there was no point in her trying to talk to me. I told my mom that I wasn't going to go to the wedding and that that was my final decision. She said that my dad was very disappointed in me and that he wasn't going to give me any inheritance if I don't go. I hung up and blocked my parents' numbers. When I went to class, my gf was there. I talked to her and asked if she had changed her mind and if she wanted to get back together with me. She said that no, she didn't, but that she was really touched by the fact that I didn't go to my sister's wedding and that she was very happy that I was choosing her over everyone else. So I asked her what she wanted me to do, and she said that she wanted me to go to her cousin's wedding with her. I said that it was alright, and that as long as she was there, I didn't care where we were. She started talking to her cousin and they said that her cousin's wedding was going to happen in a few months, but that her cousin wanted to change the date to this weekend, so I could come. She said that her cousin was alright with the idea, but that she didn't want to do anything that might hurt my feeling, and that she was alright with waiting a few more months. I said it was alright if she wanted to go this weekend, and that I would be alright if she went