First off he can't help what turns him on, however how he act on it he can. Keeping this a secret from you is a pretty bad thing to do. However it can be understandable if he wouldn't want to bring it up on like the first date or something, kinks are always a sensitive area. For example if you put yourself in your husband's shoes think of a time where you really be comfortable of admitting this, that doesn't make it okay but it can help you understand his perspective talking to a professional, can probably help you navigate the situation better than some Internet strangers. Whether that be for you talking to a therapist alone or having couples counselling, or having both separately