You will definitely not feel alone at
Island House. Back when I spent a lot of time in the island, Island House had a bit of a reputation as being one step above staying at a bath house. New owners have greatly upgraded the property making it feel more like a tropical resort and the rooms are now especially nice (which accounts for the higher prices). It is still clothing-optional and the sexual temperature is pretty high - especially around the hot tub, gym five-man shower and sauna. If you are looking for sexual adventure but in a classy setting, that is the perfect place. You can also get day or weekly passes to come us the pool and other facilities if you are staying somewhere else.
Island House hot tub, adjoining the gym, sauna, and showers. Great place for a midnight dip if you can't sleep.
An alternative is
Equator which is also clothing-optional, but not so much of a sexual destination. It's a smaller, more intimate place with a mix of couples and singles. (If you want to be more social, get a room overlooking the pool or sundecks.)
Equator Resort with its pool and multiple levels of sundecks.
I suggest renting a bicycle. The island is flat and small and easy to get around. There are lots of gay bars and restaurants to visit, but I think the main point is that the whole island is gay-friendly and the gays are everywhere. As a matter-of-fact Key West is someplace the straights go to get a peek at we fabulous few at play.