at the latest when Sean says:
"You know....if you had an 'open' relationship, he wouldn't be so stressed. He could get some quiet time to himself to think. And if you didn't want to bother him....and you weren't getting the kind of attention you wanted from your boyfriend...then you could come see me"
Ryan had to notice that this is no fun anymore but he laughs too.
Ryan is just naive or he likes the thought of 'open' relationship.
anyhow Rany becomes slowly ill by this thing.
but there seems to be almost a three-way relationship as well.