I disagree with the other replies a bit.
I actually believe that love is valuable and shouldn't be thrown away easily.
However, I do agree that by throwing yourself into her life you'll only push her away farther and she'll get annoyed by you and won't ever take you seriously again.
I would do the following:
Either call her, or write her a letter or email, or set up a meeting in person.
Be very brief, and very serious. Cut the "hi, how are you" crap and be direct and sincere instead.
Say something like "XYZ, I want you to know that I still love you, and probably will for a long time. I am not going to bother you or force myself into your life, and I will leave you alone completely. But if you ever feel like coming back to me, I want you to know that the door will be open and you will be welcome in my life. Thank you for the great times we had together, and all the best for the future -- and if that future might include me at some point you just let me know. Good luck!"
Say that, and immediately after that cut all ties with her COMPLETELY, 100%. Don't hang around her, be her "friend", etc. She'll just lose whatever respect for you she has left, and be eternally annoyed by you.
However, I feel it is important to get that message out to her very clearly and sincerely. Especially if this is the last she hears from you before you vanish from her life, those lines you said will be etched into her mind forever -- and, who knows, a year down the road, after some guy cheated on her or she feels lonely and sad, she might take you up on those words and come back.
Remember though that you can't do this half-assed. It can only work if you de facto completely vanish from her life immediately after sending her this letter or saying those words to her. This will show her that a) you still love her and WILL take care of her if she wants it, and b) you have self respect and a life of your own, and are not a spineless doormat or creep who will come crawling after her, or a puppy toy she can call whenever she has noone better to chat with.
Whatever you do, good luck. I know this is hard, and can be sad.
