This is a perfect description of what it's like. It seems to happen in episodes, too.
Every time you think you've built up some kind of bond (not anything special, just a typical everyday person-to-person emotional bond), there's another episode around the corner to reset it to zero in the blink of an eye for no apparent reason.
I was in a years-long relationship with someone with BPD, and eventually what I realized is that time doesn't strengthen anything with them. Nothing builds up over time, there's no foundation being built, you are always one instant away from being nothing to them.
Time can make you a recurring candidate for bizarre episodes of infatuation and idealization after you've left. But no amount of time you spend with them will ever meaningfully strengthen whatever bond you think you have.