why can't Natsu, Jellal, and Gray tell her they tình yêu her?

Well I think Erza all ready knows that jellal loves her.But,gray and natsu,to me, think of Erza like big sister.Remember when during the tower of heaven natsu đã đưa ý kiến he looked up to her. So in a way natsu kind of đã đưa ý kiến it. With gray I am not sure,but he feel some type of way. Gray had a weird reaction when Erza was bitten bởi Crobra's snake.