Permissibility of marrying ones student

i am 25 and the girl who is my student is 15, i am her tutor. i have feeling for her for many days, and i like here, i want nikha with her with islamic sunah, but i dont know what does she think for me i did not tell about this. i am very depressed about her, and not concentrating in my life. the feeling for her from my side is day by day increasing, right now i am not settle. i think that she will not nikha with me, but not sure, if i will not nikah with her i lost most precious think in this world and hereafter and i cannot forgive myself, in these days tears coming out from my side for her every time. please advise me, and pray for me that Allah give her to my nikha in this world and hereafter. what should i do?