I’m at a loss with my 3 yr old

I love my kiddo to pieces mind you but he only ever listens to my fiancé, every day he completely acts out and it doesn’t matter what I do to correct his behavior. He doesn’t listen he tells and kicks and hits when he doesn’t get his way with me and I’m just exhausted and tired of his behavior. As soon as my fiancé gets home he’s a perfect Angel he listens perfectly. I can’t get him to use the potty when it’s just me and him but when dad get home he goes on the potty without being asked. I’m so frustrated with him I don’t know what to do I need this behavior to stop before the new baby comes as I’m pregnant and won’t be able to constantly chase after him making sure he’s not trying to kill himself or destroy the house. I think what’s most irritating is I know he knows how to listen and be a good boy but chooses not to when it’s just me and him