You are changing.  The universe around you is changing.  Just because something was right for you in the past doesn’t mean it still is.  This could be a relationship, a job, a home, a habit, etc.

It happens to you slowly as you grow.  You discover more about who you are and what you want out of life, and then you realize there are deliberate changes you need to make to keep up with the changes happening around you and within you