British Nationality could it be revoked -not free to marry.

[Richard W]

He may have been domiciled in US at time of 1st marriage;
1st wedding was in US! not in Pakistan - does Pakistan have jurisdiction over US wedding contracts?

Why not? Scottish courts can terminate marriages contracted in England and English courts can terminate marriages contracted in Thailand. What matters is the domicile of the couple at the time of the divorce, and it need not be the same for the husband and wife. If the couple must have the same domicile, then the couple as a legal fiction will have been domiciled in Pakistan at the time of the divorce.

Now, where things get complicated is whether various jurisdictions recognise one another's decisions. There's the complication that in at least some cases, England (and I think also Scotland, but I may be wrong) only recognise 'divorce by proceedings'. There's an issue with 'bare talaq', and from the site I quoted I suspect that Pakistani case law on the matter is shifting. To complicate matters, we must distinguish Pakistan from Pakistani-controlled Kashmir.

[Casa]

Residence in Pakistan from June to October 2005 (if the case), doesn't make her domicile...it makes her a short-term visitor.