Letting Go Of "Friends"

There comes a time in our lives when we should no longer tolerate certain types of people in our circle. Finding out who our true friends are is all a part of growing up and crossing over from child to adulthood. When we're young and just starting out in the world on our own without our parents telling us who to be or who not to be friends with, it's so easy to trust and believe that everyone who wants to be your friend wants to do so because they are genuine. As we get older we learn that there are a large number of people who have their own motives. We learn that the people that call themselves our friends aren't always who they claim to be. My question is...if you've been "friends" with a person your whole life but you one day wake up and realize that the friendship is not healthy or positive in any way and only one of you is benefiting from it...do you end it?