This is an example of a 'Thinking Error', where we'll divert time and energy to a fruitless search for a reason why something did or didn't happen, should or shouldn't have happened, why we said what we did, or shouldn't have said what we did. This seems to be common amongst those of us who are worriers. Worry can be a way of our trying to control what's happening in our lives, as in
'If I think about it long enough, the solution will eventually come', or even in a superstitious kind of way:
'If I don't worry about them, something bad will happen'. We can also find ourselves replacing one area of concern for another, i.e. we'll stop worrying about one thing, and promptly replace it with another.
You may say that if these are short-term, occasional activities, that we feel we can deal with, then what's the problem - and there’s no arguing with that. It's when we persistently worry about what's gone, or about what might happen, that we can encounter problems, and it can get in the way, weigh us down, and stop us from doing the things we would like to be doing or perhaps even being the person we want to be. This is in the same area as 'controlling the controllable', concentrating on those factors and areas of our lives that we can do something about, and leaving those over which we have no influence at all. As ever, this can be difficult to do if something or someone is important to us. What we can strive for is to acknowledge and identify it if we are posing questions that have no answers - 'Why this?' 'Why that?' 'Why me?' 'What if?' - and dwelling on things that are either gone or we can do nothing about.
Whether you do this occasionally or regularly, notice it when you start to ask questions that have no answers, as a first step to putting a stop to it.
Here are some more thoughts on Worrying, with some tips on how to deal with it if it's started to become a problem.