Rejected a girl for good reasons, broke her heart. Should I apologize and how?

Hi! First , I have to say that I am very impressed with the fact that you are so in touch with your part in this situation. It takes a big person to admit when could have done things better, or admit regret. I have to tell you, I believe that you did the right thing for her. You knew what your limitations were and you did not want to involve her in what you were going through and treat her like an object. You really have cared and still care for this girl. I believe that you owe it to yourself and to her to be completely honest with her. Sit her down and have a true and honest talk. This will serve two purposes. One, it will make her feel better knowing that you just did not blow her off and did not care and two, you will feel better for having gotten the truth out. I think that this will serve to actually allow the relationship to grow. Don't be embarred about being truthful with her. She will only appreciate it and it will make her feel much better knowing that you do care. Your relationship with this girl has been long enough where you can be truthful with her. You might be very pleasantly surprised. You just may get together and work together if you should ever slip back to your old ways. She may be the best friend that you will ever have. Stranger things have happened. I wish you all of the best and good luck to you!