I'm now far enough down the road to be able to see how ridiculous it is to miss someone who never existed.
I miss the good times - but can't separate them from the craziness. I really miss the person who didn't exist.
I stayed in the relationship by justifying the craziness in my own mind and always thinking it would get better. That better person I hoped for is the one I miss.
All relationships take work, and require forgiveness. Sometimes it's difficult to know if a red flag is just a normal relationship hurdle or a BPD flag. When they start adding up, that's when it becomes a problem.