Hmmm...
No offense to anyone who thinks that was actual sexual assault, but I'm not getting that feeling from this. It feels more like Marius is using "Oh, I was confused from the charm" despite his powers and resistance to excuse being curious about what it'd be like to have sex with the super hot crazy chick. I mean, he clearly enjoyed it, even without the effects of the charm magic.
I'm personally chalking this up as "surprise sex".