Well I think thats for the best for now. In the future if he ever brings it up again, just tell him that whats in the past is in the past. If you still choose to love me then good, but I will continue loving you the same way I have been. As my cool older brother! or something cheesy like that. I think all in all that will break him from the spell and help you guys mend that broken chain in your relationship. Incest is cool in some animes and hentai, but this is real life, we are in a generation of social vulnerbility. Just do as I said and all will be fine.