Harman, is your son happy?
You say he says the other children hates him. Have you asked him to elaborate? Would he want them to like him? Would he want to have more friends to play with?
I think you should talk to the teacher. At least, she might be able to give you an idea if there are any other child your son relates to or seem to get on well with. If so, you could perhaps invite him over for a playdate?
I dont think you should dismiss this if your son is not entirely happy about school and his friendships there.
I would also encourage after school activities, there may be a sport or something else he likes that will build his self esteem and downplay the emphasis on only this one friend. Even something like Stagecoach on a weekend, if not a sport.