Oh, ye, I've been there.
My Sensei is a good looking, early 30s, non-married man and I felt we had "a click" from the moment I've started practicing.
The Sensei wasn't indifferent to me either, everything was there - the small signaling and the hidden messages (after class, of course).
It was the first time I was introduced to Aikido and I instantly LOVED the Dojo and the other Aikidokas -
They were like family : going to movies together and sitting after class in coffee shops.
I became a part of this family in a very short time.
Easy to say - I had a big dilemma.
I didn't want to loose it all, which would have definitely happen whether the relationship would have broke down on the account of one of us.
But the "what if" question kept echoing in my head...
Finally, I made up my mind to just continue as I am and see where things lead (fate usually takes us to the place we should be anyway).
It took some time, but things eventually cooled down between us.
I still like him very much and we keep teasing one another and act very warmly with each other, but no romantic feelings anymore.
It came to a point we both talked about what could have happened and the similar decision we both made.
I don't regret it - NOW it's easy for me to see that he wasn't meant for me.
A question for you - do you think your Sensei feels the same (I won't say love) affection towards you ?
Don't hurry to overrule what you feel as some people suggested in this thread - sometimes two people that share the same passion (this time it's Aikido) have a lot more in common.
Good luck and my 0.2$ advice - don't act fast, let time and a lot of thought guide you.