Me: BW, divorced, now fabulous and happy!
I agree with ama. Personally, I find this the most unpleasant thing about dating, yet I have done it dozens of times, so I am getting practice at it.
Never lie ("I met someone else," "I'm just not ready to date") because you want to live authentically and also there's a chance you could get caught in a lie and hurt his feelings worse.
Pretending it's mutual is great -- otherwise I just say something like, "I'm sorry that we weren't a match, but I wish you the best of luck in finding a fabulous lady!"
Married: 11 years, no kids
Character is destiny