Simply replace the unfilled areas such as "[]" and "[date]" with your information.
Dear [name],
Okay, so it's not meant to be. I had to try though. I want you to understand that. And I appreciate your honesty with me.
I hope I didn't wreck our friendship. I certainly didn't mean to risk it. I just felt like I had to ask, and now that you've give your answer, I hope we can move on together.
Don't be a stranger, okay?
Talk soon,
[name]