I have family, friends and parishioners in every branch. I’ve yet experienced a situation where the serviceman/woman does not get leave.
From what I see, the service tries to work with their people and get them home for things like weddings and family reunions as long as they have plenty of notice. Of course there will be deployments, missions, push times when leave is blacked out (heck, civilian jobs also have black out vacation times).
There is also the possibility that the young man does not want to go home on his leave
It just sounds as if the OP thinks that her son is going to be cut off from all connection with his family for the entirety of his enlistment, like some WWI movie. The closest thing to that today would be sailors when they are underway, but, they will almost always be able to turn on that cell phone once they get shore leave.