Betty is telling Jughead that it could of been you who murdered Jason but Jughead isn't believing her because he knows that you and him were on a date that day.
"Jughead I think it's Y/N"
"Why do you think that ?"
"Because Y/N isn't telling us where she/he was that day Jason
went missing""Actually , she/he was with me at pops on a date"
"Oh.."