Sadly this is how this shit plays out in real life, when these dumb ass husbands let their wife's do this shit. Ethan is completely oblivious to the fact that Nat and Big Dick have a relationship other then being fuck buddies. He just sets in the corner sweatin like a motherfuckin clown jerkin off watchin his ole lady get back broken by Big Dick. Not realizing she's bout to leave him, he thinks they have a rule "it's just sex". Well he's about the only one she's having sex with. You hear these dumb asses in real life whining bout the same shit, saying she broke the rules their wasn't posed to be any feelings involved. When she having these orgasms and the only person she sees in him that's only be a problem. She gonna naturally associate that feeling with him and just see you as the guy jerkin off in the corner. That basically what going on now.
When they went to that sex party he should have been able to not listen to that other fucker tell him what to do. He's not married to Nat Ethan is so he shouldn't be able to tell him"we just set back and let the other guys dictate what's happens". Ethan didn't want to do that but let his self get talked in to it. That let's you know that he has no control over his marriage. I understand what the game is meant for but fuck can't anyone think outside the box and actually give the husband a little backbone. Every story you read every game it's always the same, everybody fucks wife and husband. She does whatever she wants and the husband just is ok cause she'll give him a handjob.
I don't know what route you are playing but she is having sex with multiple people on the cuckold route, and Darrel is more central to that story cause it kicked off with him from the very first update. That is the cuckold route, not some swinger lovey-dovey route. If Ethan had a "backbone" in that route, either the route would end, or not exist at all.
And we know Ethan enjoys it, he was the one that gave the green light, even actively encouraged it and pushed Nat towards these fantasies of his. He might not be comfortable with everything Nat is doing and where it's going all the time, because Nat is starting to take her own initiatives and she is no longer purely doing this because Ethan wants too. He is no longer in complete control of what he himself set in motion. But he can't stop it now, even if he wanted too. He is a cuck with no backbone, as you put it. That is the route my friend.
Also this is a fictional porn game, stop equating Ethan and Nat's relationship to real life.
Unless you have some personal experience and would like to share with the class.