If that isn't possible, you should make a joking comment to your son that he needs to buy his own panties, that his behavior is ruining a lot of your best stuff. If his father is in any way a reasonable and understanding person, the ideal solution would be for him to have a light conversation with his son about it. If he gets the idea that there is a possibility his fantasies could become reality, there will be a huge shift in your relationship with him and I predict it would ultimately be destructive to your family. If you discuss it with him and most especially, you admit your feelings, you will never be able to retreat from that. My concern is you and where this could be headed.
Other than the laundry issue, I wouldn't be that concerned about him. It sounds like he may be a little behind the curve. Young people do all kinds of things to experiment and learn about sex although that usually happens at an earlier age than 18.
