"He works all the time, so he is tired all the time."?
Nobody works (all the time) or is (tired all the time)!
In any "long distance" relationship where both people are being sexually loyal to one another it's rare that either person would turn down an opportunity to have a night or weekend of passion together.
My guess is when he says he's "tired" what he really is saying is (he is tired of this relationship). He may be seeing someone else or may just want to be free to see other people if the opportunity presents itself. He may want to have a nice quiet evening at home alone watching sports or hanging out with some of his friends...etc What he means is,(He's tired of the routine.) He doesn't want to feel obligated to have to spend his free time with you.
"Long distance relationships" under the best of circumstances can become too much work trying to stay connected. Depending how far apart you are it may become a hassle to pack a bag and drive for hours or hop on a plane to fly for hours.
Once the "infatution phase" of a new relationship fades people tend to cut back on their efforts to "please" their mates. Instead of automatically saying "Yes" when they were seeking to impress you, they're now letting you know how they "really feel" about your suggestions. It would not surpise me if he will want to have "the talk" soon. (As in breakup) or he may just pull the old "fade away' breakup on you. I recently wrote a hub about that technique. It's when your mate slowly vanishies. Communication is key.