My brother's ex-girlfriend, a JustNo from hell

It really hit me recently how fucked up the things are all together that she did. My brothers hate her so much that we don't even refer to her by her name anymore, but for privacy's sake I'll refer to her as "That Creature", or TC for short. My brothers will be "Bill", the second oldest, and "John", the third oldest.​So this "thing" was my brother John's first girlfriend, starting when they were in middle school, either in 7th or 8th grade. In the beginning she was this cool, eccentric girl who got along great with my family, she even attended the ceremony of our oldest brother's wedding (luckily not the reception, so she wasn't in any pictures or anything). And to me, best of all she was the big sister figure I had always wanted. Being the only girl with three older brothers wasn't always a picnic, and if you're familiar with my posts about "Fannie", you'll see why I didn't have many healthy friendships with other girls. So TC was a breath of fresh air in my life, and she treated me like I was her little sister, and needless to say since she and John dated for a few years, I grew attached to her. I even used some of my birthday money one year to buy us matching plush key chains of a cartoon character we both loved.​​And me, being the doe-eyed kid I was when TC and John started dating, had thought that they would be together forever and get married some day. For their first year anniversary I even wrote a poem about them referring to them as a knight and princess (lost to the sands of time, and shit was it so cheesy and stupid). Between my normal meter being broken (thanks to Fannie) and my naive nature, my brothers wound up hiding a lot of things from me when shit started hitting the fan.​Because it's been such a long time I don't entirely remember the timeline, but some time after John and TC broke up (due to her weird, controlling behaviour) she started trying to get Bill to date her. Saying she had always been attracted to him, John didn't have to know, tons of red flags that screamed, "CRAZY ALERT, PROCEED TO THE LIFE BOATS."​​Her harassment became so bad that eventually, one day Bill snapped and called her. When she didn't answer he left her a voicemail telling her to leave our family the fuck alone, and if she didn't then she would be sorry.​So what does TC do? Calls the cops that night, and they came a'knocking around midnight, waking us all up and infuriating my parents. TC had claimed that she had a phone call with Bill that day and he threatened her, saying things like he would fuck her up if she ever came near us again and she would be lucky if she didn't get killed. All lies. TC had merely deleted the voicemail, cried crocodile tears to her parents (her mom was just as bad as she was, and completely enabled TC's fucked up behaviour) that Bill threatened her life on the phone, and her mom swooped in and involved the police.​I don't know what happened to TC when her mom found out she had lied, but no charges were ever filed against my brothers or TC. All I know is when the police confronted her about her lies, she batted her eyelashes and got away with it, claiming trouble with her bipolar medications cuz "they messed up her head" sometimes. (And a side note, her inability to properly take her medication is a part of what made her and John's relationship fall apart. She did used to take it very religiously, but then just stopped. We still have no idea what the hell happened there.)​So she managed to get away with harassing my family because the police fell for her little "woe is me, these boys are being mean to me" schtick.​Somehow, she backed off after a while. Then cuz we wound up making friends with friends of hers at our high school (TC went to a different school then us), TC and John did the whole "just friends" thing and let bygones be bygones. By that point TC had been showing she was more stable now... which was short-lived. Eventually she started trying to get back together with John, and simultaneously trying to get together with Bill despite Bill having a girlfriend (who, also, was JustFuckingNO, but different story). All while assuming Bill and John weren't telling each other that TC was trying to get together with one another again.​And while TC was doing her best to hide her crazy from our friends, she was successfully hiding it from me and playing the older sister role to me again. Despite everything I had missed her quite a bit and still loved her (again: broken normal meter), and since I was familiar with rug-sweeping and my brothers seemed not to have a problem with her anymore (which they were hiding from me) I felt like our surrogate sisterly relationship had picked back up again where we left off.​So while I wasn't the same innocent kid I was when I was 11/12, I was just glad to see the TC I had known and loved that suddenly made a 180 when I was 13. She was clinging to this idea that her and John would get back together, and even set him up with a prom date in their junior year under the assumption that they wouldn't like each other.​(Setting up that blind date wound up being the best thing TC ever did in the years we knew her, because John and her got married this year, and my now-SIL is the best big sister figure I could have ever asked for, leaps and bounds beyond TC.)​Before TC had even set up John with my now-SIL, John had briefly dated a girl he'd been friends with since middle school, "Allie", whom he had a crush on for a while in high school. But TC convinced her to break up with him after like a week or so, and to go out with her instead. They dated for a few weeks tops, then broke up, and after that TC was convinced they were soulmates. Allie died not long after (omitting how for privacy) and it wasn't until recently that it was revealed that TC had been harassing her and stalking her, online and IRL, trying to bully her into getting back together, while also claiming they were soulmates. After Allie died, TC claimed she lost her soulmate to anyone who would listen. From what I hear, she's still saying this after almost ten years. Obviously she still isn't entirely stable.​So the last time I ever saw TC or spoke to her, she really broke my trust. She invited me to go to an anime convention with her, and since we couldn't afford a hotel room we commuted to and from the city it was in by train. It was a 3-day convention, and on the morning of day 3 (during which I had a much-anticipated meet-up with an online friend of mine who was the same age as me) it was past the time she was going to pick me up so we could go to the train station, and I kept calling her but she didn't answer. She texted me a flimsy excuse and said she couldn't make it anymore, and she was sorry. I hadn't been to that city before until I went with her and she knew that, so even if I wanted to go on the last day by myself I would have trouble finding my way around and couldn't afford a taxi to the convention center. It was also way before I ever got a smart phone, so that wasn't an option either. I was only seventeen and I considered possibly going by myself, but in the end I knew it wasn't a good idea.​​After TC broke my trust, I started seeing her crazy more clearly. And when I told my brothers I didn't think our friendship would last anymore, they told me all the things they had kept from me to save my feelings. How she had been swinging back and forth between trying to get with Bill and getting back together with John before her obsession with Allie began. It was mind-boggling.​Recently, after going through these old memories, I realized TC did something that left me with mental scars that I'm still dealing with today. She was the first real big sister figure in my life, and after she hurt me twice like that, it made me put up my protective walls and not trust other girls as sister figures for a long time. It even caused me to be very closed off around my now-SIL for the first few years of her and John's relationship, and when we did start to get closer for a while I thought I had a crush on her. But I realized recently that when I start forging close relationships with people in ways like that, I started wondering if I had a crush on them. It turns out that it was like a coping mechanism, where if I had a crush and was rejected, that was easier to deal with then forging a sisterly relationship only to see it destroyed the way it was with TC. Going through that made me even think for over a year I was in love with my best friend; when I confessed to her it crushed me, but I got over it and we're still close and I still love her with all of my heart. TC damaged me in a way that no young girl should be, and I was just collateral damage. Her obsessions with my brothers and Allie were deeply unhealthy.​​I have to say this much, though. Bipolar disorder is manageable, but when TC stopped managing herself, that is when everything went to shit. TC is unwell when she doesn't take care of herself, and last I heard she still isn't taking proper care of her bipolar disorder. I can only hope that with time, she will take better care of herself. I don't know if what she did can be construed as what it's like when you have manic episodes, but it doesn't excuse everything she did. She hurt so many people and burned so many bridges. I hope eventually she can see what she did was wrong. Her mental illness isn't her fault, but it isn't an excuse either.​​Getting this off my chest has been helpful. I think I might delete this after a while, but just writing it down has helped see it really is messed up.​I was a little vague with details for certain reasons, so sorry if it seems to be lacking information.