Not sexually attracted to my boyfriend?

This is very personal and a lot of TMI about my sex life.

I’m not sure what to do. Every time we get into bed, he acts like a middle schooler seeing boobs for the first time. It’s such a big turn off. He knows I like bdsm (I’m a sub/switch), but I’m always the one doing all the seduction (even when he’s the one who wants sex, I have to initiate it). The most he does is place his hand on my throat, literally with no grip at all. He always has this giddy grin on his face - cute, but not sexy!!! I love this guy so much, we have been together for about 3 years but I’ve brought it up before, probably a year or two ago. I have struggled with asexuality in my teens, but right now I still get horny a lot just not towards him (or anyone else). I only ever come when I masturbate. I want to want him sexually, but I just don’t. I’m so confused and really don’t want to hurt him.