Aw babe, that's rough. But it seems like this could possibly be a good chance for you to get a little more in touch with yourself. I know it would be hard for me to not see my fiance for three months (or would
it...hmmmm...nevermind) but surely your boyfriend is not the only thing you have going on in your life? Like I always say, the boyfriend is an accessory, not the whole outfit! Maybe you need to strengthen your independence a bit and find a way to be happy by yourself. There have to be other things you can focus on during this time, like your career, spending more time with friends, taking up a new hobby you've always wanted to try, volunteering.
I know once you are used to somebody it is really a jolt to suddenly be without them for awhile. But there is so much more to life that you can concentrate on, so don't dwell on his absence, just find more interesting things to fill your days