So some people say that time is the great equalizer. I would like to pose another metaphor for time: Time is the great revealer as well. I have found this to be so true in so many cases. I say this because...you only learn the true side of people over time. Let's think about this for moment. Generally, people put on a their best foot forward when they first meet someone. It is only with time that people regress and fall back into who they "really" are. I can remember people telling me that you only know someone truly after you have lived with them. While I'm not advocating living with all your friends so that you "know" them better there is some truth to that saying. For some people, this is not a bad thing. However, for some this process can be a rather eye opening experience for the people that are witness to it.
In the end, people always change or rather evolve. In same cases they devolve. The best thing I have found to do is to try your best to no take the changes personal. Everyone changes and it's extremely hard for the person to see themselves changing in the process. the best thing to do is to buckle up and hang on and be the best friend that you can be. It can be hard. But honestly if you are true friends then what else can you do?