Here's a little secret.
It doesn't matter.
I am being perfectly serious.
Relationships end. A lot. Most relationships end. It's the most probable conclusion, to not be together forever and ever. This has nothing to do with the family unit, who's in the White House or whatever. It also has nothing to do with the overall morality of a society. If a person lives for 100 years and meets someone as their mate at age 20, then there are 80 years for things to end before death, and only a moment for things to end at death.
So don't sweat the ends of relationships.
I know they hurt, and I am not dismissing your feelings. But you don't have to pick apart why it ended. It did. Blame the numbers if you must blame anything, and find a way to move on. Don't dwell on it and do a post mortem