What Rebel8 said: "It sounds like you are asking us to advise you on how to cheat on your wife without the mistress feeling guilty."
Your marriage may be in bad shape, but you are a married man. Behave accordingly. In other words, man up!
What can I do, and keep her secure in her faith?
If your "wonderful JW gal" really is a faithful JW, she does not want to be romantically involved with a married man. If she is found to be engaging in "loose conduct" with you, she will experience "the humiliation of that whole process", as you put it. Would you really want her to go through that? A little local gossip is all it takes to bring that on.
want to discourage me from finding some happiness
If you really are "looking for happiness", you will do it properly and honorably. Your own post shows your misgivings about this. Be honest with yourself.