Second, if the marraige failed due to being too devoted to the ministry, then he failed to manage his household well.
You make two serious arguments. One the construction of "husband of one wife" and the second his ability to meet the other, independent tests of 1 Timothy 3.
The first depends on whether the requirement is to be a "husband" of (at least) one wife or a husband of not more than "one wife". I don't know of a Biblical view that this prohibits single (never married) men and widowers from the pastorate. The text really offers no clue on this issue. I take it from your comment that you believe it does prohibit single (never married) men and widowers from the pastorate. Why should that be?
The second is a more interesting question -- and more difficult. The full passage says,
"The overseer then must be above reproach, the husband of one wife, temperate, self-controlled, respectable, hospitable, an apt teacher, not a drunkard, not violent, but gentle, not contentious, free from the love of money. He must manage his own household well and keep his children in control without losing his dignity. But if someone does not know how to manage his own household, how will he care for the church of God? He must not be a recent convert or he may become arrogant and fall into the punishment that the devil will exact. And he must be well thought of by those outside the faith, so that he may not fall into disgrace and be caught by the devil's trap."
You essentially argue that even if (and I don't know the facts) his wife divorces him because she is emotionally unstable and unbalanced, this reflects on his ability to "manage his household."
Perhaps, but a husband has precious few tools left in modern society for dealing with an emotionally unstable woman. [It could be argued that phrase is a redundancy.] Wouldn't that require that one demonstrate that there was something within his power to do to calm her instability which he hadn't done?
If those were the facts -- and they were shown -- I would definitely be with you. I think I would need to know more.
Others have argued that he should have left because he earlier said he would. Suppose he was merely trying to "manage" his unstable wife by making that 'promise'? Or that he was mistaken in his understanding?
The biggest indicia here that he should go -- to me --is his son's resignation. Why did the son think he should go? Nobody is talking about facts, but presumably the son knows some. And that is troubling. Is the son speaking out?