I have, but it's something I tend to think about pretty much anyone I find interesting (not necessarily in a sexual way primarily). For me this is just curiosity, like I can be curious about anything. But for my current T, I do have some erotic transference to him and that brings it up in my mind more than with someone I don't find attractive that way. It's not obsessive though. I don't know anything about his sexual habits though so it's all just imagination.