i know this is an old thread but their were lots of people posting about the sensei's side of this dilemma, so i thought i'd post my thoughts as well
i am an instructor and have found myself very attracted to one of the senior students in our dojo, she is not my student but rather trains under the head master in his advanced class, the two of us have trained together for over a decade and we are friends first and foremost.
im not in love with her, at least not yet, but a part of me wants to be, i really dont know what her feelings for me are, chances are she sees me as an older brother which is great, we have known each other since we were kids, we grew up together trained together, and there is no relationship i respect more than that of a brotherhood of arms.
i dont date students as a personal rule, as an instructor i try to set a good example and hold myself to some rather strict if not harsh personal moral standards, and as a flawed human failing to meet those standards results in a tremendous amount of guilt. hence i am cautious with situations like this.
as her training advances and we spend more and more time together both on and off the mat i find us growing closer as friends and cant help finding myself hoping for more.
with that said i have not expressly told her how i feel as i dont want to make things awkward for her but i have also not tried to hide it, in my opinion its fairly obvious how i feel, though no one has really noticed, mostly because they are all focused inward.
so to students and sensei alike i can only suggest this, being professional does not mean being void of a heart, just follow your path and if it brings the two of you together then wonderful and if not the you will find your journey taking you in a new direction, but regardless do not try to force a relationship where there is none, because the risk of loosing a dojo or worse ruining your training is too great.
a relationship is a path in and of itself just as your training is, start with a strong foundation and master the principles before you attempt to learn greater things, in the same way, start with a friendship and understanding of each other and let life take its course.
it takes patience, self discipline, and an empty cup, good luck and may the universe treat you well