You're looking to host an adult forum, be it a specific fetish community, or just as a platform where you share explicit pictures with each other, but you don't know.
Home to the largest adult hosting provider on the Internet. We allow all adult content. When it comes to sexual preferences, we are very liberal.
Do you have this forum already? Where that is hosted? If not - you can start on shared hosting (just make sure your web host do not mind.