I cannot wrap my head around this, and therapy isn't working. Please help

[Lomacks]

Hi all, this is my first post here and I have been lurking for a couple of months now. I have been too afraid to post on the off chance that her family or herself will see this post, but I simply don't care anymore. I feel broken.

I was brutally discarded in June over something so minor, ghosted/blocked on everything and she immediately got back with her ex before me only 1 week later. Our 2-year relationship felt like it meant nothing, that I meant nothing.

So for some backstory, my ex was diagnosed in her very very late teens with autism spectrum disorder but she also exhibits every single trait of BPD more so the quiet side, she also has childhood trauma from both parents (more from her dad).
(if anyone would like me to explain further on the traits or trauma, I shall do in response but I'm willing to bet everything I own that she has it comorbid)

Throughout the relationship, she has tried to break up with me numerous times over the most trivial things that make no sense, things she has taken the wrong way or just simply double standards. But the most recent one blindsided me the most as she was saying she wanted to marry me a week prior and the night before she left, still said she loved me and acted as though everything was okay.
After us having such a nice night together, she goes to her mother's house to visit the following day and tries to break up with me again over text (she never did it in person and would always wait to be away from me). Here is what triggered the breakup.

I had finished my first year of university and was moving back home with my parents and would commute to uni for years 2 and 3. And my ex moved in with us (The house was more than big enough and we were given the attic room). My mother said to us that we could both live there rent-free and she would also buy us a car to share to drive to university and back (My ex is going to my uni doing a similar course but starting her first year this September when I go into the second year) and the deal was that myself and my ex only had to split and pay for food and fuel for the car between us. We all agreed on this.
And since moving back to the house my ex wasn't helping to pay for anything, I was constantly blowing through my university loan paying for the fuel in the car and food shopping or days out. Whenever she had money, all she spent it on was herself and mostly on cannabis. She smoked a hell of a lot. She also asked to borrow money from my student loan for the drugs (Which I agreed to because she said she would pay it back).
One day I asked her for some money towards the fuel whilst filling up the car and she agreed, but I never saw that money, 2 weeks passed and she spent a further £300 on cannabis again.

I brought this up to her over text whilst she was at her mother's house and said that it was upsetting me and that it felt like she was prioritising the drugs, given the fact I lent her money when she needed it and she wouldn't give me a penny back for the car. And she didn't like it one bit! she immediately got angry and called the whole thing off. Came to pick up everything from my house a week later and then I found out that she was back to dating her ex again a week after that, and I think she's already moved in with him too.

Here's the part that bothers me the most and I can't get over it.
She told everyone, me, her family, all her friends, my friends and the whole of Facebook that her ex was abusive/toxic and that he r*ped her.
She even went as far as to write and produce a song about the SA, and it is still on her youtube channel, which was also shared on and around Facebook.
Why on earth would you go back to that? especially after such allegations?

It also bothers me that his family are welcoming her back with open arms not knowing what she has accused him of. This is the 3rd time she has gone back to him after attempting and failing other relationships and each time she has left him it has messed him up mentally to the point he has needed severe therapy. I can't understand why they would be okay with her going back again.
I have found his family and I have been so tempted to reach out and share the song she wrote and warn them as they are completely unaware of the allegations. I'm just so sick of her living in my head rent-free 24/7. And the therapy isn't working.

I'm also too stressed to go back to uni as she started a smear campaign against me and tried to turn my uni friends against me. And I also know I will have to deal with seeing her there and her (once ex) who she will no doubt bring along to dangle in front of me. His sister goes there too and is in my year which I only just found out. I just can't escape her. I haven't been away from her long enough to process and deal with everything and I don't know what to do.

[Turkish]

A "dual-diagnosis" (mental illness+substance abuse) is tougher to deal with than either on its own. I'm sorry that you're dealing with a smear campaign.

Whatever her ex is getting out of re-engagement, it sounds like you're stronger than him. 

What do you think that reaching out to his family might get you?

[Lomacks]

Peace of mind mostly.
I can't cope with them not knowing the truth about her allegations. His mother really cares for him and knows how bad she damaged him when she left the last time, but she has absolutely no idea about the allegations made. Maybe it would be enough for her to push him to leave for his own safety, especially if I provide the evidence using her song on youtube and messages from mutual friends who are also confused as to why she's gone back to him. As they also know the allegations she spewed.

The guy has either, quit his band in order to be with her again (the band is really successful at the moment too) or they've kicked him out for dating her again because they also knew she messed him up. So in a way, if what she said was all a lie, I feel sorry for him. And it seems that way given the fact she's gone back so easily.

If she had gotten with someone else completely different after our breakup, it wouldn't have bothered me so much. It's the fact that he's her ex who she left before dating me, so it feels like she was never over him through our entire relationship and has been trying to find ways to leave me for him constantly.

[Turkish]

My ex got in contact with her ex when we were dating. She didn't hide it. It was hurtful. It's not uncommon to reach out for emotional validation and be oblivious of the hurt it does to others.

[Lomacks]

It really hurt, and more than any relationship I have ever been in before. Even in relationships where I have been cheated on etc.
I have a strong sense of justice and I'm trying so hard every day, but a part of me just can't let this slide.

[alterK]

Lomacks, it seems clear that you are describing a mess you cannot fix. You have no idea whether your ex is telling the truth about anything, and the longer you stay in the more of a victim you will be.

You deserve praise for the sympathy you have for other people in this drama. Surely your ex is suffering too. Such people do, a lot. But if you put on rationality glasses, difficult as that may be because your emotions are so intense, you will realize there is nothing you can do that can help to solve these goofy problems, and that you could easily make things worse.

I suggest, hard as that will be, that you detach, pull back and put your effort into healing yourself. That won't be easy, especially at first, and if you can't totally avoid meeting these people again the wounds may be reopened many times. But do whatever you need to get your head back into shape, and that means fixing yourself, not trying to fix others. The more you heal, the less pain you will have. Good luck!