Yeah this is a tricky one, can say i have been in an almost similar situation myself so i can see where u are coming from..
You dont say how long he will be away for, is it so long that it warrants breaking up?....if it makes you so upset to not have him close then you obviously feel strongly for this guy, its hard enough these days to find someone decent who you really care about and cares about you, id try and keep hold of him if i were you, enjoy to the fullest the time you have left together and use the time apart to build up your friendships with your close friends and family.
These days its so easy to stay in touch with a loved one every day, he might not be next to you and in your company but it doesnt mean you have to feel apart, you will know what to do when the time comes, good luck!