Simply replace the unfilled areas such as "[]" and "[date]" with your information.
Dearest,
The past [number] years have been more [adjective] than I could have ever hoped for. Now that we are in the [period] of our relationship, we couldn't be closer. We can read each other's mind and we share so much [feeling shared] with one another. You are not only my [relationship status], you are my best friend. Yet, I feel the need to reclaim you as my lover. It is time for us to rekindle some of the flame we had in the beginning.
Beginning [today/tonight], and for as long as it takes, I am rededicating myself to you. This will be the first of many exceptional evenings. I have made some special plans for us. Consider this your formal invitation:
Your presence is desired at [location] at [time], [casual/formal/black tie] attire.
Yours truly,