I think most, if not all of us have gone through this at some point, and to varying degrees.
It is hard, very hard, as you are experiencing now. Throughout our 4 years doing the LDR, we had several periods where we were both so down. We always knew we'd wait for each other and see it through (I'm moving there in two weeks!), but the day to day could often be a drag. We really tried to be "up" and positive for each other and focused on happy things, rather than whining to each other how lonely/sad we were. Oftentimes we'd pick a topic of discussion for the day. It could be as serious as politics/religion or as silly as the best toys we ever received for Christmas. We tried to make each other laugh every day. We were silly as hell (especially at our ages 44 & 50). We encouraged each other to go out, see friends and not mope around the house. It also helped give us more topic of conversation when we would talk about our comings and goings and nights out with friends and family. We tried to live our lives as if the other was just in the next room - we'd update each other several times throughout the day what we were doing, or funny things we heard on TV, or a simple, "I love you" email. Sometimes we'd just have a "rant" day where we'd unload on each other everything that was bothering us. Those days often made us feel better as well!
Resolve yourself to the fact that there will be a wait, and you will get through it. Be silly, be happy, make him laugh, tell him your deepest thoughts, plan "dates", surprise him (a card via smail mail with lipstick kisses), but also live your life. It will make the time go by much faster.
Good luck to you, SMILE, be happy in the fact that you found someone wonderful to love, and that this is just a temporary situation.