A few things to consider:
1. is he married or does he have a girlfriend? This may not be immediately apparent. I trained with one guy for 3 years (not someone I found interesting "that way") before I found out he was married. He just never, ever talked about his wife, and she never came to dojo social events.

2. How long have you been training at this school? Weeks, months, years? If only a short time, you may find your feelings change in a couple months or even less time.

3. Dan-ranked people that flirt with the newer students are not necessarily good candidates, especially if there is a pattern of this.

4. This is more or less the same situation as being attracted to someone in your office that is of higher status than you.

5. what kind of person are they OUTSIDE the dojo?