Welcome to the boards, smollSexnerd!
So one thing I think would be good for you to think about before entering this conversation is this: if things continued as they are without changing, how long would you be willing to stay? Another six months? A year? Five? Ten? For the rest of your life?
Sit down and seriously, actually think about this because it will give you perspective on what you're looking for from this (series of) conversation(s) and help you answer the question about not knowing what to do if he still isn't willing to change his thinking and beliefs regarding sex and kink.
Next, work yourself up to having this conversation. There will never be a smooth, naturally-occurring, and perfect time for this to just come up. So schedule a time when you two will have time to have a private conversation and make that the time which you will bring this up. Accept that it will be kind of awkward and feel weird to bring this up - and that there's nothing wrong with that. Think about what it is you want to discuss but don't plan on him having specific responses because you cannot control what he's going to say or how he's going to react. Keep what you want to discuss to a reasonable limit of things (if you have too many subjects, they'll get lost and the conversation can get confused), such as: "can we discuss our attitudes towards sex and how we foresee this working between us".
You cannot talk anybody out of what they think if they do not have an open mind and a willingness to hear and change. What you can do, especially just out of one conversation, is set boundaries with each other on what's okay. For example, your boundary might be "you don't make negative comments or shame me about my sexual preferences even if you disagree with them - you simply say that you're not comfortable doing that with me and we either discuss what you would be comfortable with or change the subject". His boundary might be something like "you don't tell me about your friend's sexual fantasies or activities".
It's up to the both of you after that to work out if these boundaries really work for you and if this is still a compatible relationship for you both.
I would encourage you to give up on the idea of convincing him to change his mind - I think that's likely to result in more frustration and upset for you. Even if he does change his mind, I don't think it's a good way to approach a conversation with the attitude of "this is about changing your mind" instead of "this is about having a conversation", especially with someone you're in a relationship with. You're going to have a lot easier time talking with him if you discuss with him rather than if you lecture him or try to be his educator when he hasn't asked for that. Say what you have to say, hear what he has to say, see what sort of effort he's willing to put forth regarding this subject, think about the boundaries/compromises you both want/need about this, and judge based on that if you can accept this part of him or whatever it is he can offer regarding this and if you'd be happy in a relationship with him including this aspect of himself, however it turns out.
I don't know what the outcome of this or these conversations will be. If it does work out, that's great! But it if doesn't, remember: we can love people who are not good for us to be with. Sometimes love isn't enough to overcome everything else that is a part of a relationship, such as communication and respect and acceptance of each other. It's okay if this thing - even if it's one thing - is too big an obstacle to overcome. You don't have to force yourself to live with someone who has beliefs that makes you physically uncomfortable just because he has many other good qualities.
And if you can't even bring yourself to have this conversation to him? I think that speaks to a larger issue in this relationship (you're afraid to have an honest conversation with them) that definitely needs addressed.