Both you and I know that the love and passion in our relationship is long gone. We are no longer interested in meeting each other. It has become more of an obligation as a couple rather than by choice.
I have been giving our relationship some thought, it seems that we just do not share the same vision when it comes to our life goals and future hopes. Our exchanges seem to be going in opposite directions, with opposite beliefs. You deserve someone who can give you all the love that you need. Unfortunately, I am not that special person for you.
[In addition, you were spotted dating another [man / woman] on [date] at [venue]. I am happy for you to move on to the next stage of your life with someone else.] I am just writing to formally put an end to our relationship, which has been long overdue. I guess someone will have to make the first move.
I will cherish the fond memories I have had with you. I wish you all the best in the future.