Do some research and explain to them that the ever evolving technological environment is no longer just for those who are lonely and depressed.
I wouldnt worry about them its your life your and adult do what makes you happy
You can't stop anyone from holding an opinion unless you're prepared to change your actions to suit their expectations. I don't know if I'd be getting "intimate" with somebody online (or even in person) within earshot of anyone else, parents or otherwise. Of course, if you're in your own space, then you can do whatever you please.
It's none of their business. Get your own place. :)