What should I do?!? Should I tell my boyfiend what I found out about his dad?

[Happy Holidays ♥]

So I was on my boyfriends dads Facebook because he posted some picture of me and my boyfriend and I ended up just looking at some of the pictures he posted. I don't know how but eventually I came across pages he followed and I couldn't believe what I saw...it was all these porn stars and half naked girls. Then I went to his likes and there was more...I don't know if I should tell my boyfriend..I mean he has two sisters and his dad is married to his mom...we're 20 by the way and have together for over a year. I'm freaking out because I didn't want to know this! He has a little sister who's 12 and this just grosses me out and I don't know what to do. Now that's all I'm going to think of when I see him..what should I do?! Please help
I came upon it by accident, I wasn't stalking....It's just weird because I really don't think anyone knows and I feel like now I'm hiding this big thing and I'm going to feel uncomfortable whenever I'm around him and he's always telling my boyfriend how attractive he thinks I am
To me being married and having a family means you shouldn't do things like that...I don't feel like its right