I have known of people who never thought that. There are some people who see themselves as having been “made for each other”, and they never have doubts.HomeschoolDad:
Every married person I have ever known has this thought at one time or another, often many times. Since we do not marry saints, we marry humans who can be annoying at best.“What in the world was I thinking ?” could be a strong indication that this was never a real marriage.
After the rosy glasses of new have cleared one sees the warts. Does not have any impact on validity of the marriage.
No, all by themselves, such misgivings and regrets don’t affect validity, but as I said, they can be symptomatic of underlying things so grave, that they could call into question the validity of the marriage. And people who are happy and contented in their marriages never question whether the marriage was valid or not.