First – The world will not come to an end; however, you may need to re-learn that which you thought you knew about the subject. This blog can help.
Second – There has been no offense committed. If you found out the hard way (by an unexpected encounter with him/her nude) you must realize that he/she is probably relieved not embarrassed. Therefore you have committed no offense to him/her by seeing him/her naked. For a Naturist, the most difficult part is hiding from people. It is contrary to their beliefs although often necessary due to the misconceptions and prejudice associated with Naturism. If you found out though a conversation of confidence, you must realize that he/she is not trying to offend you by confiding. He/she is being honest and inclusive with the hope that you will except him/her as they are.
Third – Your friend is thinking “I am glad that is out of the way, now I don’t have to hide” but you are faced with a decision. Can I accept this news and still remain friends or not? Friendships should not be discarded so easily and if you are so puritanical and gymnophobic that you are considering doing so, you may need to seek help to find out why. My suggestion is for you to at least do some honest research on the subject with an open mind.
Forth – Ask questions! Communicate openly. Tell your friend how you are feeling and ask their suggestions on how to deal with it. They have been through this before.
What to expect
It is natural to look, especially when you are not accustomed to nudity. However, it is not considered polite to stare. He/she will not be embarrassed. Naturists conquer body image issues early (improved body image is a key goal). Your friend will not expect you to undress (although you would be welcome to) to accommodate his/her beliefs and he/she would surely appreciate if you did not obligate him/her to cover up for you. Your mutual friendship will likely grow stronger and closer with the secret out in the open. My experience with informing friends and family has been good. More than 90% accept me totally. All of those that want me to hide from them have experienced some abuse in their life that they have not yet faced. At least 40% have utilized the opportunity to try skinny-dipping etc. with their Naturist friend as there is no safer way to try. At least 20% (when informed) confided they too were Naturists and had not informed others. As of this writing I have lost no friends on having been informed.