She needed a place to stay while she has been fighting with her boyfriend. So I offered to let her stay at my place. It's just me and my girlfriend anyway.

She's grateful but is taking advantage of me, eating all my food borrowing money, coming back late nights from parties. She never ends up bringing people over, but at night I can hear her talking to people all the time and I swear a few times I heard her masturbating...

Well we have 2 bathrooms, but only one has a shower/tub. so she uses it all the time of course. it's connected to my master bedroom where I sleep. I woke up late one night needing to use the restroom, heard the shower going and assumed it was my girlfriend. I just sneak up and open it up to scare her and ... it was not my girlfriend, aparently she was at work still. So there my sister is standing trying to cover her chest and pussy while the water pours over her body. I pause for a second, stunned by the sight, she was stunning, my cock instantly hard which she darts her eyes to and notices.

I quickly snapped to reality, shutting the curtain quickly and told her it was an accident thinking she was my girlfriend... I had to pee still and now with my cock hard making it not easy.. I apologized and asked if I could use the toilet.. it was awkward and quiet. I swear I could see her trying to take a peak at my cock while I was peeing...

I left apologizing again... I'm not laying in bed with my cock hard... She just went back to her room. I wonder what she is thinking... I can't believe my mind is racing with thoughts of me fucking her and watching her suck on my cock... is that wrong...

Even if it is... I want more...

I'll try and get some rest and see how awkward things are tomorrow...