Two good people can still be bad together. Not every ending needs a villain.

The search for a villain is a way of making an ending make sense. Sometimes there is one. Often two decent people simply bring out the worst in each other, through timing or temperament or the particular way their habits interact, and no amount of investigation produces a culprit. That is harder to accept than blame, because blame at least gives you something to do with the feeling.

You can let an ending be true without assigning fault, including to yourself. When people ask what happened, it is fine to say it was not working. Keep what you learned about the combination rather than building a case about the person.