Personally, I try not to identify with a game's characters, that way I don't care if they get humiliated or worse, it's not easy sometimes but more entertaining to play. On one hand, we all want Ethan to be successful in his marriage and be the rock that anchors it firmly to reality while exploring and expanding the limits of their mutual union. While on the other, some of us would like to see him fail miserably, losing his mate, to his rivals.
If I were writing this, I would steer it in a way that their union remains strong while they enjoy themselves with their temporary sex partners. One path in particular, where Nat wants Ethan to try to seduce Riya. It could be that Nat, Riya and Ethan are in bed with each other and Riya isn't the shy waif anymore, engages Nat with some full-on lesbo action. Later Riya admits she always was attracted to Nat, and she thought the only way to get to Nat was through Ethan. Later they add Darrel to Nat and Riya's playtime, therefore Ethan would be double-cucked!