Watching 10-year ex fiance spiral downwards with the guy she cheated on me with.

I'm just gonna rant and if people chime in with similar experiences or words of affirmation, that would be pretty cool.

My ex (25F) and I (25M) got together in high school and spent 10 years together, 2 of those engaged. We had our ups and downs and she was my best friend and I was hers, or so I thought. Over the years we pushed and supported each other through school and achieved our dreams of getting our degrees and moving to the city. We spent about 5 months together in our new life in the new city before she cheated.

We had recently gotten into going to raves/EDM shows. We both had a past of doing drugs/partying recreationally and we had fun. I felt like I always had a mental line to where that lifestyle felt like too much, never really went on multi-day benders or whatever. With her, I felt like that line was always blurred. She did have an addictive personality, some past demons, and would sometimes turn into that "crazy" party girl. She was also super smart, hardworking, and creative. I loved how kind, sweet, and funny she was. I was never super controlling of her behavior and figured she'd get it out of her system. We we're/still are young and I wanted her to live her life and have fun.

Well, one night we met a friend of a friend while we were out, and about a month after that, she cheated on me with him. I could tell she was acting differently during that time. More independent, started working out out of nowhere, posting more pictures, talking about him randomly, etc. Took me a week to pry it out of her after it happened. Once I learned, I left and started my life over. Hardest thing I've had to do, I'm 5 months in and still healing.

She immediately moved on with him/others. She maybe was sad about us for like 3 days, but covered up all of it with partying/drugs/alcohol. I guess she's like addicted/obsessed with this guy now and they've been living this lifestyle. Friends I've talked to don't even recognize the person she is, and neither do I. She hasn't found a job in her field and works as a server. She told me hasn't even been searching. She does a lot of coke just always has a bag of ketamine and takes bumps before sleep? I guess she crashed her car into his yesterday and told me she could've been arrested 3 times and it's fucking Christmas day. She told me this on the phone and asked me to take in our cat cuz she doesn't even want to go to her apartment. And she's all sad and crying cuz she thinks she messed up with that same guy. She knows this life makes her miserable, yet she won't do anything about it cuz she just wants this guy. Just last year we were spending Christmas with her family, celebrating life lol.

Obviously, all of this stings, and a portion of me hates her. I'm not jealous or hurting in the way I used to. Now I just really miss my best friend and my partner. I have since the beginning of this whole thing, but that's what has stuck around. I feel like it was all ripped away so suddenly. And now I just have to watch her spiral lower and lower. Ik people say no contact and let them go, but I was with her for over a third of my life so far. That's not just something you can cut out. I want her to wake up so badly. Not cuz I want her to be with me, I let that pipe dream go early on. I just want her to be happy and healthy, whatever that means for her. (maybe a little validation would be nice too lol)

Before people ask, I've been going to therapy for a few months now. I've found new hobbies and I have a good support group of friends and family. I'm learning to live alone and love myself and my life again. It's a journey but I think I'm finally starting to make it over the hill.