I'm sorry this is causing you so much distress. If it helps you feel less down on yourself, human sexuality is incredibly varied, and people can get aroused or have fantasies about all sorts of things, including things that are (or feel) very taboo. So, finding a particular thing arousing doesn't make you perverted or bad.
All that being said, since this is causing you so much guilt when you think about it, it may be worth exploring other areas of fantasy that don't trigger that same feeling. This article has a ton of tips for walking yourself through different fantasies: How to Approach Sexual Fantasy and Desire on Your Own Terms
. How about taking some time in the next few days to try them?