It always seemed to me that those intense feeling from deceptive affairs were due to “getting away with something” while your unwitting partner stayed monogamous. In other words, honesty would have freed your partner to examine their own pursuit of other partners and many people aren’t ready for that. More people have affairs than practice enm, and I’ve thought this is why. But the sheer charge from the lie may be the fun, too, as you say. That’s just one kind of intensity, of course. I’ve never lacked for intensely emotional and erotic experiences by being honest.