Relationships

Are so fickle sometimes. You have relationships with some people that mean the world to you, others not so much, and yet they seem to stay around? Why is that?
I am talking about all sorts of relationships between friends, family member, ex's, all of it.
When there is differences, and someone won't look at themselves to see how they are making someone feel, how do you know if or when to end it?  Does anyone ever know, or do you just make a choice and stick with it, hope that it works out for the best?
There has been a few people lately who have decided to step out and I must say goodbye. I guess everything happens for a reason and I must trust that all will work out for the best.