Hey HealingTee!
I ruminate on the good times sometimes too. Personally I find that recognizing that those good times were only as good as they were because of the contrast to the bad times and loneliness I was experiencing after the breakup helped. For me, being in that state of mind where I held the good times in high regard made emotional recovery incredibly difficult, it's so so hard and whilst you're in this mode, it's hard to do anything but allow time to pass to help which can be excruciating.
I fully know the reality of what life would be like with a BPD partner and it’s not the kind of life that I want for myself.
It's great that you've arrived at this conclusion, it is true. An advantage I have over some people recovering from the relationship here is that I did manage to experience relive some of those 'good times'. Every time I had a 'good time' it was balanced with a sour feeling, because I knew it would end again. It got to the point where the good times no longer felt good, and I had proof that nothing good could ever come of the relationship and the cycles would carry on forever. I'm someone that learns the hard way and got a taste of what that reality of life would look like first hand to confirm the idea which gave me quite a jump start on the recovery. If you ever do feel like you doubt that statement being true - I can confirm with first hand experience that it is true.