A guy told me he's in love with me and I don't feel the same way. What do I say?

This guy and I have known each other for about a year, and we casually dated for about two months. We really liked each other, but both of us had agreed not to make it a serious relationship because he was moving away. We just wanted to have fun and enjoy each other’s company. He moved and everything ended on a good note. About a month after he left he started texting me again and we began to talk every once in awhile. Then, out of nowhere, he told me through text that he is in love with me. Even though I think he is a nice guy and a good friend, I don’t feel this way at all. It’s even more ridiculous because we never even see each other anymore; he lives halfway across the country! I have completly moved on and I don’t know how to let him down without hurting his feelings. Any suggestions?