TL;DR my long distance boyfriend of one year has been doing erotic roleplay as an anime character with his friend online, and is rating random girls' photos. He doesn't know that I've known the whole time. I've been twisting myself into knots trying to excuse it but there's really no getting around the fact that this is cheating. How do I confront him about it? What do I say?
Throwaway because I'm too identifyable on my main account and I want to keep this anonymous until I work out what to do. I wrote a big two thousand word post about this but I deleted it because it contained too much extra detail.
We met online about two and a half years ago, hit it off as friends and got together after chatting daily for a year. We've now been together officially for a little over a year. At the start of our relationship he didn't really try to hit on me or do anything sexual, which was a bit of a bummer but I understood. I also knew from his x feed that he was a pretty horny guy, so I assumed he was doing something with someone else from the start (which was fine at that stage, I thought that we just weren't anything that serious and maybe things would change after we met in person). He has since admitted to me that he does role play "sometimes", but I have good reason to believe this is an understatement.
He is very active in NSFW/Rule 34 art communities, I know he's made a lot of friends through that because he has been doing it for years and he has mentioned it to me before (although he never goes into much detail). I am okay with this, I have no problem with my partner looking at porn. I watch plenty of porn too, I don't consider that to be cheating on it's own. My issue is that he is engaging in smutty roleplay with one of his friends. I didn't say anything at the time he admitted it to me because I was slightly in shock (I guessed that he might have been, but it was still a shocking thing to hear come out of his mouth) and I assumed that meant we weren't anything serious at the time, so I had no right to tell him what to do anyway. But when I went to visit him about 6 months into our relationship, he was constantly whipping his phone out to role play or look at rule 34 on his x feed. Dinner with his parents? Smut. Lunch with his friends? Smut. Waiting in line? Smut. Literally every spare moment we had. It made me feel so invisible. Recently I even found his posts rating porn stars. Looking is one thing, but it grosses me out that he's spending his spare time rating random women's bodies on the internet.
After the trip he told me that he had a great time, that he's been replaying the whole thing in his head, that it felt like a dream to have me there. He has no idea that I saw what I saw (even though he wasn't being subtle about it at all, I don't ever intentionally snoop on my partners and I still saw all the raunchy things he was saying to this other person). Despite it all, I feel the same about him. I miss him desperately and I want to see him again so badly. This post is about an issue I'm having with him, so I know it sounds really terrible, but we do spend a lot of great quality time together, I feel safe opening up to him in a way that I've never really felt with anyone else. He's one of my closest friends and I love him so much, I'm very hesitant to let go of this relationship but I know I have to if this keeps up.
All the while he has been telling me he loves me too and he sees a whole future with me. His parents love me, his friends were so excited to meet me (clearly he told them a lot about me), and I want nothing more than to have a future with him too but it can't be like this. I love him dearly, he's a good man and he's always there for me when it counts. We've gotten each other through some rough times and he's everything I could have hoped for in every respect except for this. He's everything to me but I can't stay with a man who thinks this is okay while he's in a relationship. I'm looking for more committment than that.
How do I talk to him about this? What do I say to him? I don't want to hurt him, but I can't go on like this forever.