Facebook doesn't work for me anymore with my son - he has 'come off it' so no joy there for me! However, I glean more from Flickr pictures, as to what they are all doing at any one time. My son has lived in the USA for quite a few years now and it is something that I have had to get used to, but I just have to check the photos often, to see what is happening. If none appear, I expect the worst, just like you with Facebook. I think it is a normal reaction by us Mums.
We try and talk on Skype at the weekends and it is lovely to see my two grandchildren plus my DiL and the dog and we have come to an understanding that if the Skyping hasn't taken place, that I text my son and he talks to me on the way to work, early in the week, on 'hands-free' and we can have a good long grown-up chat and we can be quite open with each other. I, too don't like to bother them too much, as they have their own lives to lead, but I can't help but worry, especially if I am a bit down, as I was yesterday!! (It does help to talk to others in the same predicament.) I find that friends whose families have stayed close to them geographically, have no idea of what we go through and often can be thoughtless with comments. My grandchildren were both born abroad, so I have never had them nearby, so I know no other way of being a Grandmother. We have had some great holidays seeing them and have seen a lot of the USA whilst out there. My son will always live in the USA - I don't know about your family?
(New to this so not up-to-speed with the abbreviations!)
All the best and try to keep busy. Luckily the world is a smaller place these days, as they say.....but it is hard to remain up beat, especially when they first go away - it gets better and we learn, mostly to adjust.