why was gregor behaving in this manney

manner*

I assume you mean "manner," but even so this is a difficult question without proper context. The Metamorphosis is a complex novel with incredible depth into the human situation. A good place to start when asking about Gregor might be as such: Why do I behave like I do?--in an ultimate sense.

Well that doesn't answer my question.

He behaves in this "manner" as he feels very isolated from his family and how his dad is always abusing him of how useless he is. Moreover, he is secluded in his room without having a chance to communicate with his family making him feel more isolated and miserable. No one doesn't seem to bother communicating to him either because they are scared, angry or annoyed.