How do i tell my boyfriends dad to not watch porn?

i practicaly live with my boyfriend and i went on the comp one day n checked the history ( i know i shouldnt) i saw loads of porn sites and i was gettin angry coz i thought it was my boyfriend but i checked the times and we were out every time it happened, i love his mum as if she were my own and i dont want him to watch porn... it makes me feel sick, i also dont want my boyfriend to watch porn coz his dad does sort ov thing.(he dosent though) but yeah i went to chek the history yesterday and it was deleted, im ok with comps so i checked the cookies to see the sites he went on, there were loads over 20 . . . i also noticed he had accounts with 2 sites where you can talk to other sl uh ts and stuff, i just hate it, it discusts me, and i dont think its fair.. id want to know if it was happening to me. . . so .... What Do I Do ?????? help xxxxxxxx