Very Horny Sister

I'm the youngest of 3 and my old brother is in the Navy and overseas, my sister was married but her husband died in a single car accident, he was drunk and rolled his car down a hill. I'm live the closest of all our family and after funeral and everyone returned to their own homes, I was the one who my sister relied on. She found out she was pregnant shortly after the death of her husband. The baby girl will be their first child, without her husband wages she couldn't afford to still rent the apartment they were living in and so moved in with me. I've bought a rundown 3 bed Ranch style house and slowly doing up. With my sister living with me, she took over the cooking duties as I'm a lousy cook her words. As her pregnancy proceeded, she started getting restless and I later found out she was very horny. So much so one night she joined me in my bed and asked to fuck her. I was a bit shocked at first but fucked her anyway. She moved into my room next day and we've been fucking regularly ever since. The baby is due in late June or early July, her hormones are running wild I think is why she is so horny. I don't care why she is horny I'm enjoying it while it lasts.