Why does my Love goes to hide in a cave by himself periodically?

My adopted sweetheart and I have a long distance relationship for about 5 months. Things are going well but there's something I noticed from the very beginning:  He can be incredibly emotionally connected, sharing deep feelings, love and attention, showering warmth and care one day.  I feel so loved at those times it makes me long for more. However, sometimes when we contact each other, even the very next day, things can be starkly different.  He might be distant, formal and cool. Feels like a complete disconnection.  When I ask him about it, he tells me he's aware of the disconnection. He just doesn't know why he does it exactly.  Does anyone recognize this?  Why might this be happening and how can I help?  When I ask him if he wants me to leave him alone at those times, he says no, he wishes for me to come and get him out.  Anybody has an idea?