Why does Sylphie accept Roxy being with Rudy within minutes?

Like obviously she took a couple minutes but when I watched it and when I've seen others watch there's a similar "wait what? reaction when Sylphie said like I would do the same thing and she doesn't blame Roxy and I thought he was gonna have sex with someone when he was gone anyways. Like why does she accept her so easily and not get more angry with Rudeus? Like I get there's polygamy but even with the mushoku Tensei world what Rudy did I think is still considered unfaithful