sister in laws comes to stay

My wife’s sister Sarah recently left her husband and had nowhere to stay so has moved in with us for a while.She’s drop dead georgous and she knows it.I’m self-employed and often sleep in while my wife heads to work bout 8.This leaves me and Sarah alone and It’s turning out to be very exciting.While my wife is gone Sarah ponders around the house in tiny shorts and tight tops with no bra underneath.I soon realised this was for my pleasure as she wears baggy clothes while my wife is home.One morning I got up to go for a shower.Sarah usually sleeps in late so I assumed the bathroom was free.I walked in but to my shock there was Sarah,completely naked and dripping wet,just after coming out of the shower.”don’t just stand there staring,pass me a towel”she said.I handed her the towel but couldn’t take my eyes off her perfect 38DD tits.”I’m very sorry” I said and turned and left.I went to work that day but couldn’t get Sarah out of my mind.That evening Sarah carried on as if it never had happened.If my wife Ann found out she’d kill me.
The next morning I was ready for more action.I stood by my door which was half open waiting for Sarah to get up.I was naked with my hard cock in my hand.Finally I heard her door open so I jumped on my bed,pulled the covers slightly up and pretended to be asleep.I left the covers down enough to show off my hard-on.Sarah passed the door but as I peeped through one eye I saw her double back to look in.She wispered my name to see if I was awake but I pretended to snore.There she stood with a tiny towel wrapped around her in my doorway staring at my 7″ cock.I was loving it.I kept pretending to snore and slowly dropped my hand and started to stroke my cock.I could see Sarah open her towel and start to rub her pussy.I nearly exploded but she must have realised what she was doing and carried on towards the bathroom.I lay there in shock after what had happened.I know I should have follawed her but I chickened out.I plan to do the same tomorrow morning but this time I wont pretend to sleep and see what happens….