I'm sorry! It is going to be tough, I'm sure.
There were a few things that really helped during my husband's deployment. We got a web cam and used that to talk to him on Skype. Your son may or may not have access to a web cam where he gets stationed. My husband didn't have one for the first few months of his deployment. The internet reliability over there really varies. If your son does have access though, take advantage of that! There is something really comforting about being able to see them when they are so far away. Another thing that really helped us was sending care packages. We sent a box every week. The kids and I would go to the store each week and buy snacks and treats for the box. Then we'd make cards and draw pictures, etc. We spent so much time working on each box that it made the week pass more quickly. Plus, my husband loved getting the boxes. Nobody else sent him packages, so it was really special when he got our boxes!
I know there are support groups for military moms and spouses. If you are near a base that deploys often, you might have some nearby. If you aren't near a base, there probably won't be anything in your area (we had that problem) but you can find them online. Sometimes it feels like nobody appreciates or understands what you're going through. Some people are very unsympathetic toward the military and it really helps to talk to people who do comprehend the difficulties you're facing. Yes, the military lifestyle is a choice, but that doesn't make the sacrifices any easier. Try to seek out other military moms that are going through deployments too, as they'll probably have plenty of advice and words of wisdom for you.
I think the most helpful thing for our family during the deployment was to stay BUSY. Our traveling and moving and family activities made the days pass more quickly and were a very much needed distraction. That is probably what really got me through it without a huge mental breakdown!
What branch of service is your son? If he's Army, try to get in touch with the FRG for his unit so that you can be included in the updates that they send out to the families. All of the branches have this kind of support but it's called something different. You'll probably feel better when you have some ideas of what his unit is doing and those updates help.
Stay strong! I'll be praying for your son! Hopefully some other military families can chime in here with some more tips.