I have noticed as the years go by that friendship changes in adulthood. As we grow up our job is to go to school and we are around our friends all the time. Often, we spend more time with our friends then our own family. Now that we are adults, have real jobs and are in the beginning stages of starting families of our own, friendships change. The relationships mature and I think the mark of a real friendship is when time passes and you are able to stay in touch in spite of not seeing each other as much as you would like and you are able to pick up where you left off. We may not have 'playdates' anymore, or be roomates and go to the bar every weekend but it is understood that we are undoubtedly bonded to each other. We know each other inside and out and will always be there when needed. We also have a kick ass time when we are able to get together and the time spent with each other is that much sweeter.
No relationship is effortless. Some easier then others but all in all both people need to want to make the relationship work. . I think this is why our friend list thins out as we get older. In our adult years we have finally figured out what we value in a friendship, who is worth fighting for and who we are better off without.