Just because you know one person who has a particular disorder does not mean that every person with the disorder is the same as them. That's harmful and reductive, if not downright dehumanizing.
Try reading the subreddit r/BPDlovedones. They all have the same experience over and over and over again with borderlines. Haven't seen one who has had a good outcome with a relationship with a borderline. They're all there because it's terrifying and terrorizing.
The only people who post there are those who had bad relationships with individuals with BPD, the ones who have healthy and happy relationships will not post there, obviously. Just because some people have bad experiences with others who have untreated BPD doesn't mean everyone with BPD is guaranteed to behave in the same ways.
If there was a subreddit called r/lefthandedlovedones full of people complaining about bad experiences with left handed people, that doesn't mean that all left handed people are abusive.
Find me someone who has had a good relationship with a borderline. Find me a subreddit that has people with those experiences. There isn't and that's because it's universally a terrible experience.
Like I mentioned earlier, I am that someone, both as someone with BPD but also because of the healthy relationship I have with another person with BPD.
However, I see you're not really going to engage reasonably or in good faith, so I'm not going to argue with you.
Dude, maybe just accept that there are at least one good relationship. maybe the sub does not exist because relationships are usually private and intimate, esp the good ones. There’s no need to double down just because you had a bad one.