So horny for anyone but my husband

I met my husband when we were both 19, married at 23, and now we’re both 29. As I get older I’m starting to realize more of what I want and it’s awful to say but it’s not him. I lost all attraction to him years ago and we’ve been to therapy, people say “marriage ebbs and flows just stick with it, it’s normal” and I have done my BEST but oh my god.. I’m literally so turned off by him, he’s like more of a brother or best friend and having sex with him is such a chore.. I know it’s awful but I have to imagine he’s someone else to even do it. He’s such a nice guy and he’s good to me but I cannot force attraction… please help, will this ever get better?? Or is this grounds for divorce?? I’d feel so shallow for leaving because of sex but I feel hopeless.