KAGH-028 Her best friend invited me to do something lewd… Can I resist the temptation? (I couldn't resist and came inside)

My beloved girlfriend. Her friend is super beautiful. That super beautiful friend invites me over. And she does this while I'm pillowing my girlfriend's lap as she sleeps! Even though I think it would be bad if we get caught, my lower half honestly gets erect. Unable to move with her head on my lap, I get a blowjob from her friend, and amidst the excitement and sense of taboo, I end up having unprotected sex and ejaculating inside.