And if they persist in asking why, just say, "We don't feel we're really compatible." You don't have to rehash stuff, like saying, "Well, when you did this and she said that, blablabla..." Not necessary.
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein