Demanding friends: to deal or not to deal with?

Do you have a demanding friend(s) who expects more of your time and energy than you can freely give? How do you deal or cope with this individual? Or, do you cut them loose? If you are finding a trend of demanding friends in your life, what does this say about you as an individual? Are you yourself a demanding friend? Are these types also “high maintenance” friends?

I occasionally get into a situation with a friend where they start to expect/demand to see me or talk with me more frequently over the span of a week than is convenient/feasible. Inevitably, I conclude the friend is being high maintenance and deal with them as such (ie see them less, demonstrate my schedule is not as flexible as theirs, etc.). Is there a way to avoid getting to this point? How do you train your friends to respect your time boundaries?

Any comments, suggestions, stories and antidotes are welcome.