Keiyuu said he'd be coming home really late that night, but he decides to do something special for his girlfriend Ayame and arrive much earlier. But when he got there, he found Ayame pleasuring herself, and said something outrageous...

"Isn't this cheating? You like the boy in your head more than me, right?"

She denies it, of course, but he won't listen.
And so, to prove her love, Ayame masturbates in front of Keiyuu...