The hard truth is that it's more than likely a lost cause given the fact that you have a three and a half year sample size where nothing has ever changed. As such, you have no reason to believe it's ever going to. I'd say to sit down and talk about it, but it seems you have and always get dismissed.

That begs the question as to why you'd have agreed to enter into a legal relationship with him knowing all of this. Marriage isn't going to change anything. The relationship you have now is the same relationship you're going to have after signing a piece of paper.

Now, I realize I'm being very matter of fact here, but for context, I'm a guy and I'm happily married. I tell you this so that you understand I'm not being negative for the sake of being negative. I'm not at all anti-marriage. I love love and I wish you nothing but the absolute best.

To keep it simple, the two of you are fundamentally incompatible. Your sex life is honestly an afterthought in the big picture here. You've lost interest in having sex with him, because you're overall unhappy with him. Even if you started having more sex, that wouldn't change the fact that the other problems still exist. You're not being unreasonable to want intimacy in your romantic relationship, and that's beyond sex. It just simply doesn't exist here. Is that how you want to spend the rest of your life?