Wife's sister is pregnant with my child?

I am a little confused..your call her your wife but yet your not married..how long have you been having sex with her sister...at least 3 months...why would your girlfriend or wife as you call her say that you are irreplaceable so you had to leave..none of this makes any sense to me. are you making this up to see how ppl will react if you are trying to be a writer...if so this story in my opinion would definitely not sell.