Re: Being civil with your ex after your marriage
As long as the husband does not keep in regular contact with the ex-gf (thought phone/e-mail/text etc)…I don’t see this as being a problem. If they cross paths due to having the same social circle…then that’s not really in the husband’s control.
Although one thing that wasn’t mentioned in the post (unless I missed it). How exactly did the wife found out about their past? 
Personally I follow the saying “keep your friends close but your enemies even closer” when it comes to all the women my hubby comes across (especially if they’re not mothers yet). But since the wife in your situation isn’t a very confidant woman…this probably isn’t a good idea for her.