What would happen if you said it was none of her business? Or "I don't ask you everything about your activities?"
Should NOT be snotty or aggressive. If you don't have a wife like Smileys or an H like mine (who will zealously do the work for you), you may need to be more direct in that you will be divulging less information in general. Could be tricky. There have been points where I've said, "I know you want space and I don't ask you for details as to what you are doing so I am going to expect the same for myself." More often H will ask me where I'm going, I say "out" or "out with a friend" and he'll say "boyfriend" and I'll just laugh (because it is ironic that I'm actually on my way to the library to write)...
This is sensitive stuff though. In some sitches, it is very important to convey that there is no infidelity or chance of it.
