I don't think you're familiar with the hate fuck concept.
I never said Rowan shouldn't find out about her infidelity, just that the way it was done was bad. He already see her and greyhide, there is no reason for not to be possible for him to discover it and still remain with her. The problem is Alexa turning into a sexdoll while 10 other better paths should exist first.
ItsDaBoy22 made an excelent point talking about open relationship, it makes a lot of sense in a playthrough were both rowan and Alexa are corrupted with the horny disease