Friends??

I'm looking at how my life has gone these past few months and I'm wondering, what exactly makes a person a friend to me. Is that person there for me in my time of need? Do we spend time together? Does that person listen when I need him or her to? Can I always be myself around that person? These are questions that I've asked myself over and over because I've always prided myself on being very selective of who I label as my friend. What I've come to realize is that the people I've surrounded myself with over the years who I felt that I wholeheartedly trusted, loved, and cared for, aren't really the type of people who I'd consider my friends now. So, now my question is, as we grow older, experience new things, and go through our ups and downs, do my friends have to change as I change?