MC knowing about being cheated on and associated humiliation is pretty much optional, and in lot of these stories they'll remain unaware throughout. The important part is the player knows and can witness these acts with their own eyes (and experience the sense of betrayal when their virtual spouse lies straight to "their" face)
It's sort of the other way around: as the player, you can prevent Alexia from escalating drug-induced sexual contacts early on, but if am not mistaken she eventually comes to realize she has feelings for Greyhide regardless, due to their other, friendly interactions they've had. At this point i think (it's been a while) as Alexia you can choose to make this known, which leaves Rowan basically with no option but to accept they might sleep together, or to keep it to yourself and end the quest line this way.