It's All Very Simple To Them

This morning:

Me: Kate, we saw S__ and S__ last night!
Kate: Are S__ and S__ brothers?
Me: No.
Kate: They're just friends, then.
Me: No, they're married.
Kate: (confused look) A boy and a boy?
Me: Yes.
Kate: Why don't they just marry a girl?
Me: Because they love each other...
Kate: Oh, OK.