I just stumbled upon this thread. I went through something very similar with my BF who I still love and adore about a month ago. He also thinks that this is just the way he is and nothing will change. We was sexually attracted to me, but saw me as a "good girl" (though I'm highly sexual) and was addicted to porn which of course made me feel like crap in bed at times as he would compare me to porn stars and often wouldn't be able to get it up.
I brought up therapy which he was dead set against. I kept thinking "Why am I not important enough?" But it's not about that. He's scared and he's gotten used to the way he is. In a way it's sort of like a security blanket.
After the therapy thing, he started pulling away emotionally and I caught him in few lies. Unfortunately instead of owning up to his lies, he blamed me for snooping though I only snooped because I suspected something (he emailed an ex when we were on a short break).
He keeps saying I can't accept him (he also struggles with SSA).
I am upset as I love him to pieces and hope to marry him one day (he told me I was the one several times), but ultimately there's nothing I can do. It's a tough pill to swallow. I've found meditation to help a lot. And red wine.
Anyway sorry to hear what you're going through, but you're not alone and this is definitely not about you.
As for me, I am definitely going to get that codependant book. I'm thinking maybe there's a reason I attract guys like this.
Hope you are well and if you feel like it please update with what happened.