Snailshell, I'm sorry you're having these feelings.
I haven't been stupid with my life on purpose.
From what you describe here, you haven't been 'stupid with your life'. You've pursued things of value which interest you, like music. You've cared for those who needed care. Some would say this is more important than ticking boxes like marriage or homeownership.
It's a cliche that comparisons are odious, but, comparisons are odious. Your ex's relative wealth and stable lifestyle is not a comment on your choices, it is the result of her inheriting money from her parents. There is an entire structure of advertising that exists to tell us that 'having more stuff' makes us better, superior people. We all know this, and yet we are susceptible.
Your ex's new relationship is also not a comment on you and it is unlikely to be as ideal as it may be portrayed on social media. People do not change very easily - you probably know this from trying to break cycles in your own life. It is even harder for someone with a disorder like BPD. If you went back a year ago, you would see my uBPDx living an exciting new life in a new and vibrant city with his new partner (me). Fast forward to now, and that relationship has been destroyed by his cheating, lying and instability - just as his last live-in relationship in a different city, was. It's not better. It's just a different part of the cycle.
Even after how she was to me...
The world doesn't run on reward and punishment. It runs on
cause and effect. Your ex will not be 'punished' for her abusive behaviour towards you in the sense that there will be no validating authority that comes and says, Yes, she was wrong and you were right. But there will be consequences, because everything has consequences. You are not in control of these for her, only for you.
You have been trying to make good decisions. You will see the results of that, but that's different from saying 'I'm a nice person, therefore the universe will reward me'. There is a skill to being good, and part of that includes identifying disordered people like your ex and how to behave around them, and also identifying chaos or disorder that arise in your own mind (for example, when you think about your ex) and acting skillfully with regards to that.
Act skillfully, authentically and according to your values and try not to compare yourself to her (but also, don't berate yourself if you do - we don't have perfect minds). It will be OK.