Lucky for you I played the "long-distance" relationship game for a bit when my husband and I were dating. There are many ways to build the relationship, grow closer, and show love when you are apart. It would depend on what you had access to, ie-the internet, skype..etc
Personally, I would let my husband know that I was praying for him--for his safety, for strength, for perseverance, for his integrity....
give him reminders of God's love and sovereignty through scripture.
I would also write many letters--letters that were full of love and how much I missed him, letters about the future, letters about the times we shared, letters about what I was up to while he was gone.
I mailed a letter every day when my husband was in boot camp (he was my fiance at the time). This was because he could not talk on the phone or use a computer.
I would send packages when I could--comfort from home, special things to remind him of me, things to help him endure.
Whenever possible, send pictures :) Pictures that are for his eyes only!
Be faithful, and be careful of getting needs met elsewhere--mostly those emotional needs. It can be lonely and hard, and emotional affairs are very easy to get wrapped up in.
Your love and support are two things that go hand-in-hand. He needs to know that you are there for him. Knowing that you will not stray, that you are not going to leave, that you are going to keep loving him. This knowledge and TRUST will be what he needs to make it through this time apart.
Keep in mind that time apart can be one of the best ways to grow a relationship--because when you are apart--all you can do is talk!!!
Just be careful when you get back together ;)
I hope this helps!!