The reason most likely reason might be that he might have unresolved issues and he does not know the proper channel to raise them. As a result of this the only way he can express himself is through methods that do not make sense and seem stupid.
He may have "anger issues" or be a bully. You've got to sit down with him and try to work this out. Tell him you won't stay if he can't control himself. Be careful because sometimes people like him escalate and start insulting and berating and even pushing or hitting. You can give him a second chance, but be prepared to stand up for a decent relationship. Find another boy who isn't like this. Most aren't.