I know this may sound unbelievable, ....
this is very believable. as added spice, and this will give it the feel of a greek tragedy, remember that it is only a matter of time before one or the other spouse figures out something is going on. increased levels of security lead to increasing paranoia and desperation, which are possible erotic features you might want to explore.
after discovery, the story goes in one of two directions. either violence directed against you by the husband, or by the husband against your paramour. or your wife might decide to shoot you while you sleep, or do worse.
the alternative is finding out that neither spouse cares.