5 year old is a spoiled a$$hole (sorry)

My 5 year old has become the most spoiled kid in the world and it’s ruining my relation with my bf. He isn’t my bfs child but my bf and I do have a newborn together. He was this way before the baby came. He is constantly telling me and him what to do, won’t share, my bf tries to play with him and all he does is scream and whine and says he’s calling the cops. My bf will buy him a toy and he will take it and throw it in the garbage. I don’t know what to do. Taking things away, time out ect is not helping. Now I’ve gotten a call from his teacher saying my bf and I are mean to him when we really are not. I’ve been getting harder on him and I’m sure that’s why. He doesn’t act this way with his father but his father is jealous of my new relationship. Any ideas on how to get him to not act this way? He’s spoiled and has an attitude 100% of the time and I can’t deal with it anymore.