Do you ever feel like you settled?

I've been with my DH for over 15 now, married for 5 of those years.  We started dating in high school, I went off to college but we stayed together.  I felt like I changed as a person in my mid twenties and wanted to break up but he pleaded with me to stay together.  I loved and cared for  him so we stayed together.  Sometimes I feel like I became so comfortable that I just settled. He's a great guy but I'm not happy with him.  I don't want to be with anyone else nor is there anyone else.  But I'm neither sad or happy.  Just cruising through life...  I'm just curious if anyone has ever felt the same way or is in a similar situation.