I went through this when my master started doing business in another city. In fact, I was in a really similar situation because the relationship had just started out. I wanted to be fully supportive and didn't want to seem clingy. But then I realized that I could be supportive without retreating from the sub role. I told him that I wanted him to go because it was good for his business, but that I felt anxious when he was gone. I told him I felt silly for feeling anxious given our relationship was just starting out. We worked out a deal where he would call me at a certain time. He'd assign little tasks or just talk and it made it so much better.
You said your dom has trouble understanding what you're feeling, but even if he doesn't understand the reasons why, you could still work out a deal like that. Negotiate whatever amount of contact you need to feel alright about him being hours away.
Best of luck!