Should I? Or should I not?

Ok there is this guy I really like. Its hard to tell if he likes me cause he flirts with me a lot but then agin I dont know if he is doing it because im the only one around him at that time or w/e but when we flirt he always grabbs me wraps his arms around me and hugs me a lot! Anyways does he like me? Also I really like him and he knows that and like he said im like a sister to him but he said it a while back and I want to know if its a good idea to ask him out? If so what are some ways to ask him out without sayin do you want to go out. we are always around eachother at school and walk eachother to class. And I am tierd of just being flirts. I want to be his girlfriend. I need all the advice you can think of. Thx a bunch.