AITAH for not attending my abusive sisters wedding, causing her to go non contact with our family, and not trying to fix it despite my mums wishes?

AITAH? Sorry about the long post. I just need someone else's opinion on this situation because it's been on my mind lately. I explain the main event first and then go into some back story.

When I (18 at the time, F) was in my first year of university, my sister (23, F) was getting married to her partner, who I had become good friends with over the last few years as he taught at my high school. While I was happy for the couple, I let them know that I wouldn't be able to attend their court house ceremony as I had a huge group assignment (a speech) that same day and time for university, but I was more than happy to attend the party afterwards. I could not move this presentation, it was a set date that I had before their chosen date and my group and I would fail if I did not participate.

This created the largest shit storm I have ever seen. Suddenly because I could not make it, they uninvited our parents, our 6 other siblings and cancelled the party we were going to be hosting for them after the court house ceremony. Our mother was incredibly upset, and a thousand other emotions but never mad at me. My sisters soon to be husband threatened that if anyone from the family contacted them, he'd get the police involved, restraining orders, move away and take my sister with him. A whole load of threats. This was unlike him, and no one could have seen this coming. I've never spoken to this sister since, 9 years later. Over the last 2 years my mum was able to regain some contact again over email but it's mainly when the sister has a problem with her kids and needs advice.

Growing up I was pretty close with this sister, she's 5 years older than me, this is an important detail. I dont remember when this started but she use to make me play pretend with her, we'd act like we were chacters from WWE (world wrestling entertainment), except in her version, all the wrestlers had relationships with each other. I think it started as our Beanie Kids (small collectable bean filled bears that all looked different) they were the characters and she'd tell me this guy and that guy love each other, and squish their faces together to kiss or lay down on top of each other. The earliest I remember this happening was when I was maybe 10 or 11 years old. Over time this progressed to us pretending to be the people and talking to each other in secret as the characters. Then when I was in high school, she would make me pass her phone between us and write out what these characters would say and do to each other. I remember young me having to ask her what words like "straddle" and "thrust" meant as she made me respond.

This had been going on since I was a child. I didn't understand it was wrong. I thought it was just a form of playing a game at the time, a game that was our secret. When I was maybe 12, she was 17 (this is occurring in Australia where at 18 you're an adult), she'd make me be a certain character and she'd be their partner. She'd move my hand and make me touch her between her legs and rub, because the characters would want to do that. I always felt so uncomfortable with this, but she'd say it was okay, its just like what the toy bears do.

Thankfully, when she moved out to be with that guy I mentioned in the start, her now husband, we didn't really talk any more. I felt safer and didn't contact her. Eventually, she reached out to our mum and asked for me to go over to her new place. I didn't have a choice. This might have been when I was around 15, she was 20. I remember she slid her phone over to me with the notes screen open saying something like "I'm this character, hello" and then when no one was looking she'd try to get me to respond. When I ignored the phone, she tried whispering "are you -characters partners name-?" While touching my leg. I know I refused to engage in this creepy behaviour and I never went back there.

So a few years later when I had to decline her wedding due to my university assignment, was the an A-hole for not going? It wasnt just the assignment, that was a convenient but legitimate excuse. I wanted nothing to donwith her. Do you think her reaction to me but going could have had anything to do with how she treated me growing up? I never told anyone what she made me do as she said it was our secret and I was scared I'd get in to trouble. As an adult, I know this is really messed up and it's been on my mind lately because it's messed up my dating life and how I view relationships. I'm considering talking to a counsellor about this. I just can't tell my family, I've grown close with my mum over the last few years and she often says she really misses this sister and wants to meet her daughters.

I'm not sure if me reaching out to the sister would fix everything and let my family have her in their lives again. But there is absolutely no way I want her in my life. I've seen that she still writes fictional romance stories about these characters and posts them online so I highly doubt she's changed at all.