He knows somewhat. He found animal porn on my web search years ago, but we haven't ever talked about it. He might just think I was just curious. I was ashamed at first. Now I think I want to be more open about it. He is pretty open minded about things. I think he isn't going to be too shocked. I just don't know how to bring it up.
Maybe another web search with the browser history not cleared? Nothing too graphic, but something that gave a slight hint?
Take it in small steps if you're unsure of his possible reaction.