Sure it would be good to find out every little detail of why shit went bad or whatever. Reality is if they dropped the relationship out of nowhere, then something is wrong (probably with them on a seriously mental level) and you may never get those answers from the other party.
I’ve been there, but ironically I had all the answers I needed within myself. I just had to open my eyes and see things honestly no matter how painful they were. Take a step back and really analyze your relationship while taking out the emotion. Look at it as a psychological study. Create your own closure.
Sometimes that is the only option. It could be the healthier option as well…Perspective.