I learn from the book it said that if you truly love some one, let them be at their best and do not have to be together all the time. I think you already know he loves to travel then you have to learn how to accept that he may not be around you whenever you want him. This is not about you being selfish or he is selfish but about do not make him feels like you are dragging him down with your wants. Now a day, with high tech, he may be thousand miles away but still can call or talk to you face to face in the internet if you miss him...If I were you and love him dearly I will let him goes with his dream. You can not keep the bird who want to fly. Best wish