Hello and Thank You for responding. Your son may be upset because his father got remarried and you are no longer his wife. He may feel that you should be mad about that new relationship. I am not sure how long you have been apart from your son's father but I hope that he got through the break up alright. If he did not, there may be some repressed anger issues still lingering around in which he should seek counseling for: just a few sessions may help. His pediatrician can refer you to a great counselor and/or psychologist. If that is not the case and he seemed perfectly fine after you and his dad split, then there are other issues obviously.
You must tell him specifically what you expect him to do. Write it down if you need to as a visual reminder. When he disobeys or breaks a rule or goes beyond the boundaries that you have established, then he must suffer consequences. Make sure that he knows what the consequences will be beforehand. Limit his time with friends, television watching, computer time, cell phone time, video game time etc. Whatever he enjoys, take it away when he misbehaves. Then when he chooses to behave and make the right choices, he can "earn" back the fun things that he likes doing.
Currently, he seems to be the one in control. You have to get the control back and make your son realize that he cannot have his way just because he whines and is bossy and disrespectful. You are the authoritative figure in the household and he must never forget that. I am not sure if there is a new dad in the house, but if there is, he needs to give you support as well. If there is not, the discipline techniques rest on your shoulders. You just have to have the mental fortitude and courage to remain the BOSS.
Additionally, do continue to praise your son when he is behaving well and spend that quality alone time with him. That will make him feel so very special.
Hope this helps!!! Have a great day!!!