If being honest and open with both of them is of primary importance to you, then you should honor that. Be true to yourself.
I were you, I would surprise them with a visit at home, at a time when you know both of them will be there, and just walk in and say, "Look you two, we need to talk. I'm with both of you. Let's be honest with each other about what's been going on or I will leave right now and neither of you will see me again." And mean it. Walk out and don't look back if they are unwilling to discuss it.
Because although love and sex can be gratifying, you are obviously tormented by the dishonesty. You need to maintain your integrity, not give in to their stupidity. Really, all these secrets and whispers is just a ridiculous thing to have to put yourself through. I keep picturing you running back and forth between the two of them like you're in a Marx Brothers movie or French farce or something. If it wasn't your actual life it would be a comedy of errors!