He has a sever anal fetish...

So I was on the computer and stumbled across some porn, from my SO. It's like, anal fisting and prolapse and everything to do with anal. 
We do anal on occasion and I'm okay with that, but anal fisting and prolapse!!?! That makes me feel sick!  I'm worried that if we marry or continue to be together, he'll want to do these things if he is obviously turned on by and I won't want to? Are we doomed? Is doing that stuff that bad? Could I grow to love it? Is anyone into that sort of thing that can give some advice. I love him and we've been together and I always thought we had a healthy sex life. I tried to bring it up, but he just said 'Nah he just wanted to see what it was.' I dropped it because I didn't really feel comfortable even talking about it! Help!