Friendships, close friendships can be complicated, as complicated as the people in them. Friendships exist on many levels and cover a wide range of emotions. When a friendship has gone on for a long time a lot of things happen that test the people in it. If one friend takes too much it creates an imbalance and the one who is giving can become depleted and resentful.
Take a look at your friendships and make sure you are givng as much as you are taking. If you find you are giving too much, it might be time to take a break. If you are taking too much, it might time to give your friend a break.