Portland Hobby Jogger has a lot of great points. I ran in college and still competed until just before I turned 30. I lived a very disciplined lifestyle in my 20's with very little social life. I loved the training and competition.
As I got into my late 20's, my body was breaking down and after I hurt my IT band, I realized that I had accomplished about as much as I could. I didn't accomplish what I wanted (OT qualifier) but I mentally knew I had given it everything I could. I simply didn't have what it took to get to that level.
Also, I was ready to move on with my life I was building a business and coaching high school and finding much more fulfillment from helping others through those avenues than I was from my self-centered running lifestyle. I still ran with my team and with friends to stay fit and because I enjoyed it (still do), but my body and psyche needed that change.
There are two questions you should ask yourself to help with this decision.
1. Do you feel you've accomplished all that you can accomplish with running? If not, do you still have the desire to push yourself to your goals? As I said before, I realized that my body was not able to produce the goals I had set for myself. Did I want to keep pushing myself if I couldn't get to that next level? Some people keep on going while others (like me) move on.
2. What will you do with you time and mental energy if you do give up competing? I was coaching a successful team and enjoyed seeing my athletes succeed more than I enjoyed succeeding myself.
Two major factors in being happy are depth of involvement and meaning. Right now, you are deeply involved with your running and find a lot meaning from it. You will need to find something else in which you can engage yourself at the same level (or at least close). The Olympians that struggle after they are done competing usually don't have a an for their post-competitive career.
I had a guy I coached years ago that ended up being a two time XC D1 All American in college. He was a natural to move up to the marathon post-college. He ran a couple of marathons and got to about 2:21-2:22. He decided to move on with his life and give up competive running about two years before the Olympics. He realized that it wasn't worth it for him to make the sacrifice needed for another two years to maybe get to that level. Many years later, he has a thriving career, a growing family, and a very happy life. He is very much at piece with the decision to walk away while he still had something left in the tank.
Good luck in making your decision.