This is very difficult but do-able. You simply have to do it and I promise you that as each day passes and you remain faithful, it will get easier. When something in your life is not Godly, God will honor you for walking away from it. Satan will try and make you see that you can have the best of both worlds.
You don't have to tell them, either. Just walk away. (speaking of internet relationships, of course)
Rania