after a barbeque last week at my sisters house .. i took the spare room with a girl i've been dating for some time. in the early hours of the morning i awoke to go for a pee and heard obvious moaning noices downstairs, i had a quick pee and crept halfway down the open planned stairs....i noticed my sis on a sofa with her legs high and spread with a man fucking her, also i saw a older women sat at her side sucking her breast. i watched as the man shot his load over my sisters boobs and watched as the naked woman licked it off her and rubbed it into her skin...the woman then started to give my sister oral while another man stood at one side wanking himself off...i sat on the top of stairs and wanked myself off also...i came when this man took over and shoved his dick in my sisters mouth she seemed to love every minute, being licked out and giving oral at the same time. should i be ashamed or is this normal ...i'm 29 my sister is 25 ??