Well, your therapists job is not to be judgemental, and really is there to help your deal with your issues. You personally may not have any issues with your own sexual thoughts, but maybe others around you might. Your T can give you a venue to speak and discuss your thoughts and help you discover whether you accept them or not.
Many times these kind of attractions (thoughts/desires) are representative are other parts of your personality. I am not a qualified therapist, but perhaps these indicate an attraction to persons who offer no resistance or allow you complete control, and maybe the other indicates an attraction to risky activities.
I know that I'm bisexual and that I hesitated to state to my T that I have gotten aroused by seeing a male horse with his "stuff" out and hard. I was afraid that I would be considered sick or bad. My T told me that I was likely aroused because it was "forbidden" as much as having gay sex while in a committed heterosexual marriage. Just like dreams and nightmares, sexual attractions and desires aren't always black and white, some need to be interpreted.
I personally feel the best thing to do is to talk about it with your T. Otherwise, it will eat you up inside.