How do I handle my 5 yr-old...?

My 5 yr-old son has problem in gelling with kids of his age.Whenever he is playing with any kid he wants to make sure that he does what the other kid wants him to do, but when in a group he is frequently left alone and teased. At times kids turn on him even when he shares his toys and gives them what they ask for. Physically he is quiet fit but when someone hits him he does not react and get beaten quietly. On the contrary to this behavior he is very violent at home and misbehaves with us. Recently we had another child and the condition seem to be slipping out of my hand further. He has become extremely emotional and whenever I try to correct him for something he starts crying and talking to himself murmuring that he is a bad boy, also frequently telling that I don't love him. Since the time we decided to go for another child we had prepared him mentally and we have been making sure that we show our affection as many times as possible. He loves his younger brother and behaves well with him. How do i handle him.Does he need to be taken to a child psychologist.