Dear Beth,
This letter serves as my 2 week's notice of termination of our relationship. I have very much enjoyed being your significant other, and have been fulfilled in our relationship. However I find that I have reached a plateau in regards to my love for you, and as a result have not been putting myself 100% into our relationship. I feel this is a disservice to both of us, and that a clean break will allow us to both find better matches for our needs.
My last day in this relationship will be May 5th, 2010.
I wish you the best of luck in your future endeavors, and hope our paths cross in the future.
All the best,
Your ex.