Okay let me try it another way....
1. Sage and Chad are a couple for 2-3 years.
2. They have no sex at all during that time.
3. Sage discovers that Chad is cheating on her.
4. Sage confronts Chad and asks him "Who is she ??????????"
Now you seriously believe ... THAT's what she would say if Chad didnt fuck her at all ??? I mean dude c'mon, you can believe whatever you will, but it has to be within reason.
ANY girl in that spot would go apeshit on his ass and say "3 years and you never fucked me but you fuck another girl !!!".
Im sorry but it just makes NO sense whatsoever