Hi, welcome
I'm pretty sure a parent cant be denied their children by distance however this needs legal confirmation. I know my sister years ago couldnt take her child to a warmer climate (Vic to QLD) unless she had medical reason to do so which she did (Asthma). That son needs a first free visit to a family law solicitor to ensure that the children are not taken out of the country.
If its not too late you can subtly suggest couples counselling however, there is a very fine line between that and being seen as interfering.
My ex partner of 10 years had her daughter separate 3 times from 3 different partners and today she is still in touch with all 3 of those men (her daughter had a child to each). I found it impressive that she didnt get involved as she might not have maintained contact with one or more of those children. So the moral of the story is- these separations happen and best posiution to take with them is to remain in contact with the son/daughter in law as a friend/acquaintance which can be very beneficial later on if they reunite or your child or the in-law reveals to you that they are considering getting back together. eg the position whereby you are consulted in a manner that you can assist them.
Worry is non productive- except they can produce ulcers, step back, allow it all to unfold and in times of conversation about the topic be the wise parent that listens and says little but what you do say is wise and supportive. To get to the point whereby you are the first person any of them consults is the best support you can offer. Displaying any anxiety of suffering on your part is to add to their already taxing experience.
You could also consult your GP about your anxiety. We often underestimate how bad anxiety is because it wanes in severity.
I hope I've helped.
TonyWK
