Answer this please!!! 10 points best answer!! thanks?

So I like this guy at school and he is in the grade above. His sister is in the grade below me and we are really close. Now, I think that he may like me back but either me or my brother embarrasses me and my friends make jokes about me liking the dude. And my face gets really red whenever I see him, very obvious that I like him. Also, he is leaving our school after this year and I'll probably never see him again and I don't have his phone number or go over his house, cause of his sister, not him. there's only one more dance at our school and I was wondering if I should ask him to dance or ask him out. but if he says no, i'll be really embarrassed, sad and depressed case he is the grandson of the headmaster so I tried hard to bring my grades up, which I did :) so ummm helpful answers and thanks