|Sounds like a case for Judge Judy.|
If he bought the laptop for you as a gift, it's yours, not his. Since you're splitting up, why do you let him use the laptop at all? And why is he still "in the neighborhood"? And who the heck doesn't encrypt their wireless signal these days? I think you have other issues that need fixing & they sure can't be solved in a computing forum.
But to answer your question - the only way to prevent the wireless signals from showing up is to disable the wireless in the laptop. Of course, all he'd have to do is turn it back on again.