This sounds like a loaded question. Spending time away is good if you're getting sick of each other. But if you're getting sick of each other your relationship may not last anyway. To me spending time away means doing things for yourself like visiting family or friends, sports or because work requires it. But if you're strictly doing it to be away from him then there is a problem with your relationship.
You should absolutely answer his calls.
You have to know there may be nothing you can do to keep him interested if his eyes are lurking. But for someone who wants to maintain a relationship you have to try and keep things spiced up like Borat mentioned earlier. Whatever you did at the beginning if possible. Guys are simple, at least once we gain some sort of maturity. If you have a physical relationship then keep it frequent, and keep it exciting. Continue to date as if you just met(much easier said than done). Go to the movies, dinner, amusement parks, or whatever it is you all like to do to get out. Make him feel special. Compliment him, pamper him, and most importantly let him be a Man by doing the same for you. Also let him have his time with the fellas and don't nag him.