Help! 5 year old is out of control

My five year old is not disciplined at all. And it’s my fault. He is used used to getting away with everything and getting what he wants. He’s always mean to my bf, calls me stupid, tells me he hates me, doesn’t put toys away when told too, won’t eat supper at the table and always needs to be in front of the tv and so on. I always let him do what he wants and now that my bf is here and moved in he cannot stand it, and I understand why. We also have a newborn together and I think that made things 10 times as bad for my 5 year old (5 year old from previous relationship) my son screams and whines nonstop if my bf wants to try and play with him. He won’t share his toys with him, hits him

And much more and my bf is about to move out because of it.

I have been getting strict with him to see if that helps. It’s helping very little but it’s a start. I feel so mean and terrible because I’m constantly mad at him cause he won’t listen. I know I’m a terrible mom because he’s not used to being scolded for doing things and then he cries which is because he’s spoiled. Any tips on how to get him to not be so mean and start listening? Anything that worked for you?