What is the relationship between me and him?

I participate in a debate competion which needs a group of 5 pupils.As I am in form 1,I am the youngest one among them and there is a boy in form 4,which is REALLY annoying.In the group he LOVES teasing me the most,why?His reason is that he know me more than the others because we go to the same church...In the debate,he is annoying.But when we are not with the debate,he is awfully nice with me,just like a brother.He is also the type that plays SMS n when he is boring he will find me.When I am depressed,He will cheer me up.What do u all think?I need all your opinions,but I sincerely hope that it is only pure brotherly love.TQ