You've been married 16 years, tried everything to make it work, and still there's this distance between you that's like the Great Wall of China. No attraction, no connection...so how do you just say, "it's over"?
Your partner might feel the same way.
Don’t be afraid. Try to have a leave headed discussion.
Don’t drag in past fights.
Be fair, let them know you still care but that you are suffering and you know they are too.
You want them to be happy and you want happiness for yourself.