Has it been considered that perhaps things can simply stay as they are, with you and lover talking online and the very occasional meeting IRL? Or is there some pressure to get the relationship moving forward. If the the later, moving forward to what?
I have to agree that your best chances of solving the dilemma likely lay in your wife and lover developing a relationship of their own. Online being the easiest way, and there is the options of texting, voice chat, and video chatting.