When in doubt - ask him or point out to him your observation and let him share the reasons.
The speculations can be many. If you meant close (by intimately close) then he probably wants the best of both worlds- intimacy when you're in the same area and freedom to explore other options when he's elsewhere.
It sounds as though you're the one thinking about him as you said "He's in my mind many of times during the day" and that he makes you miss him. Your feelings result from your thinking (since no one can make another feel something )
Just ask him or write him an email to share your troughs and feelings on this issue.