Ooh, this is a tough one. I had a relationship that had to transition into long distance while I went to grad school, so I kind of know the feeling you’re describing. Well, I assume that even though you’re not going to be dating after the move, you’ll still keep in touch, yes? I’d suggest something like starting to use Skype now and have video chats (if your computers are capable of that) instead of calling each other on the phone, so when you move the transition kind of blurs. It’s not a stark line between “we are here together” and “now we’re not.”
Mostly, I’d suggest talking about it. Pretending this relationship doesn’t have an expiration date clearly isn’t making things pleasant, so talking about it is really the only alternative. Is there even a little bit of a possibility that either of you would consider a long distance thing? Maybe keeping the door open to that possibility will take some of the pressure off.