It is not appropriate to date your teacher because there is a power differential between the two of you. Teachers are in a position of authority and trust and it is their responsibility to maintain professional boundaries with their students. A sexual or romantic relationship would cross those boundaries and be inappropriate. In addition, it could lead to favoritism or special treatment which would be unfair to other students. If you have feelings for your teacher, it is best to keep them to yourself and find someone else to date.